Thomas Huxley invented the word agnostic, and by it he meant skepticism:
Agnosticism is not a creed but a method, the essence of which lies in the vigorous application of a single principle... Positively the principle may be expressed as in matters of intellect, do not pretend conclusions are certain that are not demonstrated or demonstrable. Link
Bertrand Russell defined it differently:
Are agnostics atheists?
No. An atheist, like a Christian, holds that we can know whether or not there is a God. The Christian holds that we can know there is a God; the atheist, that we can know there is not. The Agnostic suspends judgment, saying that there are not sufficient grounds either for affirmation or for denial. At the same time, an Agnostic may hold that the existence of God, though not impossible, is very improbable; he may even hold it so improbable that it is not worth considering in practice. In that case, he is not far removed from atheism. His attitude may be that which a careful philosopher would have towards the gods of ancient Greece. If I were asked to prove that Zeus and Poseidon and Hera and the rest of the Olympians do not exist, I should be at a loss to find conclusive arguments. An Agnostic may think the Christian God as improbable as the Olympians; in that case, he is, for practical purposes, at one with the atheists. Link
Then comes this recent video telling us all how we should define it, siding with Huxley:
I object to someone defining the words I use. The people who seek to define my words for me have power over me. They basically are claiming I cannot use a word the way I want to use the word. I can use any word I want to, so long as it communicates.
Can't we all just get along here and ask the person using a word what s/he means if it's used differently than the dictionary definition? You see, dictionaries don't attempt to tell us what a word should mean. They tell us how most people use the word.
In any case, what word would you propose to describe Russellian agnostics? There are many of them. If there is no word describing them then shouldn't there be?