|A Google-generated definition of agnostic: a person who is in between being a theist and an atheist.|
In 1869, Thomas Huxley coined the "agnostic"; the following is a retrospect statement about how this term came about:
“When I reached intellectual maturity, and began to ask myself whether I was an atheist, a theist, or a pantheist; a materialist or an idealist; a Christian or a freethinker, I found that the more I learned and reflected, the less ready was the answer; until at last I came to the conclusion that I had neither art nor part with any of these denominations, except the last. The one thing in which most of these good people were agreed was the one thing in which I differed from them. They were quite sure that they had attained a certain "gnosis"—had more or less successfully solved the problem of existence; while I was quite sure I had not, and had a pretty strong conviction that the problem was insoluble. And, with Hume and Kant on my side, I could not think myself presumptuous in holding fast by that opinion ... So I took thought, and invented what I conceived to be the appropriate title of "agnostic". It came into my head as suggestively antithetic to the "gnostic" of Church history, who professed to know so much about the very things of which I was ignorant; and I took the earliest opportunity of parading it at our Society, to show that I, too, had a tail, like the other foxes.”— Thomas Huxley (c.1885), in: Encyclopedia of Religion and Ethics (Ѻ), 1908
The following are related quotes:
“Well, I tell you, if I have been wrong in my agnosticism, when I die I’ll walk up to god in a manly way and say, sir, I made an honest mistake.”— Henry Mencken (c.1930)
“I have repeatedly said that in my opinion the idea of a personal god is a childlike one. You may call me an agnostic, but I do not share the crusading spirit of the professional atheist whose fervor is mostly due to a painful act of liberation from the fetters of religious indoctrination received in youth. I prefer an attitude of humility corresponding to the weakness of our intellectual understanding of nature and of our own being.”— Albert Einstein (c.1955)
“At exactly which point I lost my early religious faith I am not clear, but I suspect I was then about twelve years old. It was almost certainly before the actual onset of puberty. I remember telling my mother that I no longer wished to go to church, and she was visibly upset by this. I imagine that my growing interest in science and the rather lowly intellectual level of the preacher and his congregation motivated me, though I doubt if it would have made much difference if I had known of other more sophisticated Christian beliefs. Whatever the reason, from then on I was a skeptic, an agnostic with a strong inclination toward atheism.”— Francis Crick (1990), reflection on circa age 12 years 
1. Crick, Francis. (1966). “Why am I a Humanist” (Ѻ), Varsity Magazine.
● Agnosticism – Wikipedia.