I've looked at this question repeatedly over the years, and I still don't feel I have a perfectly clear understanding. The terms can be used very broadly, yet you can find very specific and contradictory definitions (particularly between people, i.e., who you're trying to communicate to). Considering this, I'd say it's almost unreasonable to use "agnostic" or "atheist" and expect it to be able to convey to someone exactly what you meant. (Or maybe I demand too much from three syllables.)
[small]Vocabulary list
nonreligion/irreligion, nontheism, apatheism, ignosticism, antireligion, antitheism, metaphysical/ontological naturalism, and various modifiers to atheism: weak, strong, positive, negative, implicit, explicit, agnostic, critical...
If you only look at one, may I recommend ignosticism? "The view that a coherent definition of God must be presented before the question of the existence of God can be meaningfully discussed. Furthermore, if that definition is unfalsifiable, the ignostic takes the theological noncognitivist position that the question of the existence of God (per that definition) is meaningless. In this case, the concept of God is not considered meaningless; the term "God" is considered meaningless."[/small]