Agnostic is one of the few common English words whose inventor told us exactly why he made it up.
Thomas Henry Huxley was a British biologist best known as a public champion of Darwin's theory of evolution. In 1869 he joined the Metaphysical Society, a new discussion group in London. Early on, according to the Huxley archive at Clark University, each member gave his position a name: Anglican, Roman Catholic, Positivist and so on.
Huxley had no label, and felt like the fabled fox without a tail. So he coined one. In his own later words, quoted by Britannica, the word "came into my head as suggestively antithetical to the 'Gnostic' of Church history."
The reference was precise. The Gnostics were early Christian sects who claimed direct, personal knowledge of spiritual truths. Etymonline says they appeared in the first century AD and were suppressed by the sixth. Huxley's word takes their Greek root, gnostos, "known," and adds the negative a-. It also echoes the Greek agnostos, "unknown, unknowable."
Huxley meant a method rather than a belief. He insisted that agnosticism was "not a creed but a method," a line Britannica quotes. The method was to hold no conviction the evidence could not support. In 1889 he published a long essay, "Agnosticism," in the journal Nineteenth Century, retelling the story of the coinage. It was popular enough that four editions of the issue were printed.
The date is slightly tangled. Etymonline gives 1870 for the word in print and says Huxley coined it "supposedly" in September 1869. A 2025 Interesting Literature article notes that the Spectator printed "Agnostics" on 29 May 1869. That was four days before the society's first formal meeting. Its author suggests Huxley may have used the word at an earlier planning meeting, and calls the evidence somewhat inconclusive.
Huxley's word, for all its scholarly Greek, comes from the same ancient root as plain English know. Etymonline traces both to the Indo-European gno-, "to know."