Looking at my Dictionary program, I see:
of or relating to knowledge, esp. esoteric mystical knowledge.
• ( Gnostic )of or relating to Gnosticism.
noun( Gnostic )
an adherent of Gnosticism.
ORIGIN late 16th cent. (as a noun): via ecclesiastical Latin from Greek gnōstikos, from gnōstos ‘known’ (related to gignōskein ‘know’).
So, a "Gnostic" is someone who has knowledge, especially of the mystical type. The word comes from the Greek word "to know". Relating to a "God" claim, a "Gnostic" is someone who thinks they know; i.e., someone thinks such knowledge is possible.
Ok, so what's "Agnostic"?
a person who believes that nothing is known or can be known of the existence or nature of God or of anything beyond material phenomena; a person who claims neither faith nor disbelief in God.
of or relating to agnostics or agnosticism.
• (in a nonreligious context) having a doubtful or noncommittal attitude toward something: until now I've been fairly agnostic about electoral reform.
An "Agnostic" is the opposite of a "Gnostic". With respect to the "God" claim, an Agnostic" is someone who thinks that "nothing is known or can be known"; i.e., they do not believe that anyone can know either way. So, it now becomes somewhat clear why a person may equate "Agnostic" with "Undecided". An "Agnostic" would say, "I do not think it's possible to know whether or not a God exists," thus they are remaining undecided on the matter.
But to say, "I do not think it's possible to know," is not the same thing as saying, "I'm remaining undecided." It's actually possible to make up your own, personal, mind on the topic, to the best of your knowledge, even in the face of no evidence one way or the other, and I maintain that just about everyone has already done so many times. For example, how many modern adults remain completely undecided with respect to the existence of Faires? Most sane people have decided that Fairies do not exist, but they do not have any firm proof this is in the case. It could be the case that all Fairies simply have a method of making themselves invisible to all humans such that you can't detect them. Regardless of this possibility, most sane people have made a decision on the matter, even though they would have to admit that they are really "Agnostic" on the existence of Fairies; this is, they would have to admit that they really really believe "nothing is known or can be known" on the topic.
Scientists and people well versed in Logic would tell us that "one can never prove a negative." There really could be an ancient Chinese teapot in order around Saturn. You can not prove that there isn't. You also probably can't prove that there is. Thus, all people must be "Agnostic" about an negative proposition. All we can ever say about, "X does not exist," is, "The statement can not be proven or disproven, thus we are Agnostic on the topic."
"Fine, but I'll never be an 'Atheist'! Saying that God doesn't exist is simply too strong of a statement and, besides, you can't prove that anything doesn't exist." Very true, but what, exactly, does an "Atheist" think? Does an "Atheist" believe God does not exist?" That is, obviously, not a very rational position, as has been shown above.
Let's investigate this term, "Atheist." What does the dictionary say?
a person who does not believe in the existence of God or gods: he is a committed atheist.
So, an "Atheist" is not a person who believes God does not exist. The definition doesn't say that. The definition simply says that an "Atheist" lacks a belief in God. In other words, an "Atheist" somehow lacks this "belief in God" which others seem to have. The "Athest" isn't saying that "God does not exist," they are simply saying that regardless of the question of existence or nonexistence, they lack a belief in that God. By comparison, a "Theist" does have a belief in God.
So, we can now create a matrix of all possibilities:
|Theist||Gnostic Theist||Agnostic Theist|
|Atheist||Gnostic Atheist||Agnostic Atheist|
I would maintain that most so-called, "Theists," are actually "Agnostic Theists." That is, they would gladly and readily admit that they can not prove the existence of God. After all, most Christians would maintain that if God could be proven, then there would be no need for faith. That is an "agnostic" position. However, while readily admitting that God can not be proven, they also have a belief in God, which is what makes them a "Theist".
I would further maintain that most so-called, "Atheists," are actually "Agnostic Atheists." After all, recognizing that the existence or non-existence of God can not be shown is central to the definition of what most people mean when they say, "God." For most people, God, if he/she exists, is outside of this universe (how can God create something of which he/she is already a part?), and as such can not be demonstrated using knowledge which is part of this universe. Being "Agnostic Atheist," is really the only possible, rational, version of "Athiest," since it recognizes that non-existence can never be proven.
For the most part, we're all "Agnostic." Saying you're "Agnostic" doesn't really say anything more than, "I don't think anyone can really know for sure," but most rational people would admit this is true from the outset. The question, which still remains unanswered, is whether or not you, personally, have a believe in God, even though he/she can't be proven. You can't use the term, "Agnostic," to side-step the real question. Either you have a belief in God ("Theist"), or you don't have such a belief ("Atheist").
If you "don't really go along with all of that God stuff," then you're "Atheist" and you'll have to admit it and become comfortable with it. "Atheists" can be good people, especially if they're "Secular Humanists!"