Huxley, who coined the word, did not consider agnosticism to be solely about God. As he put it in his 1899 essay, Agnosticism and Christianity (in response to Henry Wace's accusation that agnosticism is "mere evasion"):
Agnosticism is not properly described as a "negative" creed, nor indeed as a creed of any kind, except in so far as it expresses absolute faith in the validity of a principle, which is as much ethical as intellectual... that it is wrong for a man to say that he is certain of the objective truth of any proposition unless he can produce evidence which logically justifies that certainty... The justification of the Agnostic principle lies in the success which follows upon its application, whether in the field of natural, or in that of civil, history; and in the fact that, so far as these topics are concerned, no sane man thinks of denying its validity.
He goes on to list "Materialism and Idealism; Theism and Atheism; the doctrine of the soul and its mortality or immortality" as all belonging to the "region of uncertainty."
And in his earlier (1889) essay, Agnosticism:
Is the modern more or less complete suspension of judgment as to the facts of the history of regal Rome, or the real origin of the Homeric poems, anything but agnosticism in history and in literature?
Also from Agnosticism:
That which is unproved today may be proved, by the help of new discoveries, tomorrow. The only negative fixed points will be those negations which flow from the demonstrable limitation of our faculties. And the only obligation accepted is to have the mind always open to conviction.
This is notably at odds with the modern sense of the word. By Huxley's definition, a person with good evidence for God's existence could in theory be an agnostic and a theist at the same time. Huxley seems to have changed his mind at some point about whether or not this could actually come to pass. In Agnosticism, he avers that "the limitation of our faculties ... renders real answers to such questions not merely actually impossible, but theoretically inconceivable," but in Agnosticism and Christianity, he states "I do not very much care to speak of anything as 'unknowable.' ... I confess that, long ago, I once or twice made this mistake; even to the waste of a capital 'U.'"