agnostic is directly from the Greek, where Greek agnōstos unknown, unknowable, from a- + gnōstos known. Specifically, as first used by Huxley it's: 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.
Obviously, if you could demonstrate the proof of the conclusions, then the term no longer applies.
In that sense, it's hard to be a militant agnostic. Atheist - a certain belief that there is no deity(s), and that comes from the Greek (atheos), meaning "without gods."
That is two very different deals going down, one a caution against belief in which no proof exists, the other a certain belief, a belief just as certain as those that do believe.
I guess you can define words to mean what ever you want in an Alice in Wonderland kind of way, but in the real world, definitions are pretty fixed in fact. (And, in the real, real world of English, definitions are fixed in the Oxford Dictionary of the English Language.)
That there is, or is not, some sort of diety is not objective, objectivity can only be seen in light of the proof that can be objective or not. And, objectivity can take many forms.
Say we were having a debate about who was the world's greatest rock band. I'm going to say, the Grateful Dead, my friend #1 says The Beatles, and friend #2 says Pink Floyd. All of us can offer objective proof for our claim. The Dead played more concerts and sold more tickets than any other band. The Beatles sold more records overall (1.3 billion and counting), and Pink Floyd sold the most copies of a single record. OK, so the Pink Floyd guy is out, as two records have sold more than DSofM, now we could argue that Thriller is not strictly a rock record (and I'd agree) but that still leaves AC/DC Back in Black having sold a few million more copies then DSotM.* Now you come along and say, I think it's really Smashing Pumpkins. Based on what exactly? Oh, because you think they are the best, but there is no objective way to measure that, they never performed as much, or sold as many tickets as the Dead, never outsold the Beatles, nor did they have a single release that outsold Back in Black. So Smashing Pumpkins can only win on a subjective, and not an objective basis.
So while an objective basis can not settle the debate, it at least can frame it. Subjective debate is never framed any further than the person's own thoughts.
* you can almost always win a free drink in a bar with this one, for some reason everyone assumes that DSotM is the largest, but the RIAA does not agree giving AC/DC the edge at 49 vs. 45 million. Thriller has done 110 million, (more that DSotM and Back in Black combined) and it's going to be mighty hard to top that.