Early 17th century: from ecclesiastical Latin deicida ‘killer of a god’, or directly from Latin deus ‘god’ + -cide

https://en.oxforddictionaries.com/definition/deicide

The definition says to kill a god. This would have been one of the thousands of various gods, goddess, and demigods.

I come from a long illustrious and distinguished philosophical tradition. One embedded with a deep abiding cultural ethic that has been habitually, and instinctively devoted to deicide for centuries. Classic Greek Cynics, intellectually and logically, killed off many of the gods, goddess, and various demigods back in the day.(middle third century-bc to the Council of Nicaea in 325 ad) Let's be clear, however, these ideas of a "god" having been killed is incorrect. Only the idea that they were some type of a  G*d.  Big  "G"..  G*d. has been altered.

They are now tourist attractions, art works, or even an icon on the sides of sneakers. See the goddess, Nike. As I type this, I have a winged Greek goddess on my feet. The goddess Nike is no longer said to be an active force in the universe, she has no influence on the society we live in. She is now a corporate symbol of athletic dominance and big bucks endorsements.

In Greek Mythology, Nike was the Goddess of speed, strength and victory. Also known as Winged Goddess, Nike is most often pictured as having wings

https://greekgodsandgoddesses.net/goddesses/nike/

As far as I remember, Nike was never attacked by the cynics, she was not offensive to their concepts or seen as a societal hindrance. She was harmless in their eyes. The first attacks were on communally disruptive deities or psychologically projected abnormalities, manifesting themselves in a divine form. Nike, for example, died out because of disinterest, not hostility. While hostility to another's beliefs is mostly uncalled for, dangerous beliefs, that harm individuals or societies should be logically challenged.  Me, I'm good without a pagan temple to the castrator being located down the street from me.

These acts of deicide, however, likely lead to the sudden fall of the cultural traditions and religious practices for all the citizens of the Roman empire by 400 ad. Setting off a catastrophic series of events. (Europe would not recover till the Enlightenment)  While the early Cynics were wholeheartedly, gleefully even, engaged in their intentional acts of deicide, they had neglected what came next. They had no answers for what came next. They had not really fully thought it out or considered it even as a possibility in over 500 years of thought. Not a single one could have predicted the coming of a monotheist religion arising and cornering the market, as it were, on the G*d concept.  Soon spanning the entire Europian continent as well as within the conscience of a far larger humanity. It was an event well beyond their scope of understanding. They knew of monotheism but did not view the concept of monotheism as man-made. The concept of the logos was as an observable feature of nature to the Greek Cynics. They did not attack it viciously, they only observed it, and debated what it could possibly mean. This concept did not rank high up on their outrage meter.

Monotheism or the pagan concept recognizing it was discovered by Heracleitus, it was the first concept of a single G*d in what was then a thourally pagan world. (The Jewish peoples were monotheists, as were the Zoroastrians at that time) This was centuries before the Septuagint (Greek translation of Jewish religious text) was introduced to pagan thought.

 The idea of the logos in Greek thought harks back at least to the 6th-century-bc philosopher Heracleitus , who discerned in the cosmic process a logos analogous to the reasoning power in man. Later, the Stoics , philosophers who followed the teachings of the thinker Zeno of Citium (4th–3rd century bc), defined the logos as an active rational and spiritual principle that permeated all reality. They called the logos providence, nature, god, and the soul of the universe , which is composed of many seminal logoi that are contained in the universal logos . Philo of Alexandria , a 1st-century-ad Jewish philosopher, taught that the logos was the intermediary between God and the cosmos, being both the agent of creation and the agent through which the human mind can apprehend and comprehend God. According to Philo and the Middle Platonists , philosophers who interpreted in religious terms the teachings of the 4th-century-bc Greek master philosopher Plato , the logos was both immanent in the world and at the same time the transcendent divine mind.

https://www.britannica.com/topic/logos

How did the path to pagan inner faith deicide begin? Well, it was Diogenes of Sinope (a slave most all of his life) Who had a most revolutionary idea. That all of the ideas shared with him were the ideas of Men. He searched and could not find any with a divine origin. Not in any of the ideas claimed as having a divine origin, could he, in fact, find one worthy of being called divine when strictly logically examined. It was only later in life (late 50s early 60s) that he broached the subject with others. For a slave, Diogenes was permitted great leeway due to his mastery of philosophy. He was called the dog once, while sitting at his master's table, by a guest. He asked if the guest really believed who he was addressing was a dog? The guest applied in the affirmative. Diogenes rose from his master's table and proceeded to urinate on the leg of the guest.  Saying if you call be a dog, I may, therefore, be tempted to act like one. This did not end his life strangely enough. Perhaps it encouraged him to test the limits of free speech for his time.

At some point, later in life at another party held by his master, Diogenes got up to speak. He lavishly praised the gods, and goddess as any good pagan was likely to do. Profoundly praised their mighty powers, pontificated greatly on the benefits that they bestowed were surely all sure signs of their presence all around us. So they should be honored and deeply revered. No one could question that. Applause met him all around, it went over well. Until that is, he raised a second point. Since they are so powerful he said, let them be introduced into what is now called the arena of ideas.( A Greek concept of philosophic debate.) And then let them stand on their own merits. Surely we shall learn something, perhaps a valuable lesson he added, with a sly look in his eye

Of course one can not start with the  "Dii Consentes", or pantheon the 12 main components 6 male gods,  6 female goddesses. You must build up to toppling the big dogs of theology. Don't punch down at the  lower levels divine hierarchy either, aim a little up the chain at a feared or disliked deity, like Cronus, son of Gaia. Cronus the castrator of Uranus. (Uranus was the father of Cronus) Not a lot of good physiological imagery or attributes associated with the castrator. If you are new at the deicide game, make sure you pick the right target. Zeus, for instance, might not be right target for your first time out of the gate, trying to knock off a god

Was I picking the first deity to try to "knock-off" in such an inglorious manner? It would surely be the castrator. Who will defend the castrator? As it would be more than probable that he would be asked to self-castrate, as a sign of his personal devotion to the castrating deity. (some really did)

What this meant was, for the very first time ever.  Concepts supporting the ideas of gods were now competing for acceptance in the arena of ideas. When those ideas or others, are introduced into the arena of ideas, they become fair game.  A philosopher can grab any idea by the "figurative" throat that he so desires and then violently shake it about, stamp it into the ground if he liked, viciously pummel it, again and again. Just to see if the idea has any substance.

Cronus was impolitely tossed into the arena of ideas, forced to fight fiercely for his own existence.  Cronus was found lacking in substance, appealing attributes, or redeeming communal values. His rights to be deified were questioned and then roundly rejected by his philosophical examiners. The mocking and Greek memes of humor directed at him diminished the appeal of Cronus in the larger community of believers. Soon the castrator was a "god" without devotees and soon forgotten left to perish on a theocratic dung heap.

I believe that Nietzsche was using a similar philosophy in his failed attempts at deicide toward the monotheism of Europe. Good ideas die hard. That is why he failed where other succeeded. Monotheism has been in the arena for over one thousand years. Here is where I believe Nietzsche failed and admitted it. The most effective attempts to kill an idea, or the claimed divinity of an idea, are most effective when launched from within. Nietzche and Hitchens, in my opinion, were the two most effective at questioning if a concept or idea can be divine or G*d. Neither could complete a deicide as planned. Nietzche admitted as much here. He admits humanity's morality is metaphysical and is not found in nature by him.

Taken from Friedrich Nietzsche's, the Gay Science chapter named, "in what way we, too, are pious"

"Will to Truth" that might be a concealed Will to Death.  Thus the question "Why is there science” leads back to the moral problem: What in general is the purpose of morality, if life, nature, and history are "non-moral"?  There is no doubt that the conscientious man in the daring and extreme sense in which he is presupposed by the belief in science, affirms thereby a world other than that of life, nature, and history; and in so far as he affirms this "other world" - what?  Must he not just thereby deny its counterpart, this world, our world?  But you will have gathered what I am driving at, namely, that it is always a metaphysical faith on which our faith in science rests - that even we seekers after knowledge today, we godless anti-metaphysians still take our fire from the flame lit by a faith a millennium old, the Christian faith, which was also the faith of Plato, that God is truth, that the truth is divine. 

http://www.lexido.com/EBOOK_TEXTS/THE_GAY_SCIENCE_FIFTH_BOOK_.aspx?S=344

Translated to pagan philosophy.

that even we seekers after "the logos" today, we "knowledge-less" anti-metaphysians still take our fire from the flame lit by a faith a millennium old, the " monotheistic" faith, which was also the faith of Plato, that "the Logos" is truth, that the " knowledge of the logos" is divine.

“Words, as is well known, are the great foes of reality. ”— Joseph Conrad

https://plato.stanford.edu/entries/aristotle-metaphysics/

So those who find their beliefs under attack (no matter what they are) fight for them. Don't let them die.  Deicide has happened 100,000s or 1,000,000 of times in human history. People are still trying. There is nothing wrong with that. It just makes belief stronger when we defend our concepts supporting our beliefs. Strong beliefs thrive, weak beliefs perish.  If you believe some concepts of god or gods are harmful or dangerous in your societies vigorously challenge them,  contest them openly, try to purge them or commit deicide upon them.  But know, that in this, the arena of ideas all contestants must be equal participants.

This icon or object of worship in philosophy (Diogenes of Sinope) was a truly "disgusting dude" and complete failure as a human being. But he made up for that with his gift of wisdom left behind. Human "prophets" are many times found to be deeply flawed, he, more so than most.

 Diogenes of Sinope taught that you should never take the words of Kings, Rulers, Emperors, Priests, Shaman, fortune tellers, auguries, wise men, politicians or prophets at face value.

They all have been known to have a greater propensity to tell a lie than the average man. Investigate everything they say before placing your belief in them and their words. Else you are likely to find yourself made a fool of, time and time again.

Truer words were never spoken!!