Is the term "atheist" the only one where you demand that the person being labelled an atheist has an understanding of the term
No. I would hold it to be true of all self-descriptive labels. The problem the insistence that babies "lack a belief" in the same way atheists often use that phrase. It implies an ignorance both of how language works and how the mind works. It often involves the claim that atheists don't even know what this "god" concept is that they are denying. Such a view is completely misinformed. Using the word "god" as atheists means that their possession of a concept of it is required by biology and by every linguistic model of language use:
"ideas, concepts, and the like are represented by neural activity. The exact circuitry involved is uncertain, but it suffices for us to assume that some
stable connection pattern is associated with each word, concept, schema, and so on"
Feldman, J. (2006).
From molecule to metaphor: A neural theory of language. The MIT Press.
A central control task in neuroimaging studies that involve e.g., response times for lexical processing, or for tests of categorization, is the necessity of nonsense words. This is so vital because any other word is represented conceptually in the brain in a taxonometric network of relations to other concepts believed to have similar properties:
"word presentation activates functional webs, including multiple reverberatory circuits, that fail to become fully active if pseudo-words are perceived.
Physiological differences between words and pseudo-words have been found in numerous studies using both electrophysiological and metabolic neuroimaging techniques (Creutzfeldt, Ojemann, & Lettich, 1989; Diesch, Biermann, & Luce, 1998; Hagoort et al., 1999; Price, Wise, & Frackowiak, 1996; Rugg, 1983).
Thus, it is uncontroversial that the brain distinguishes between words and similar but novel and meaningless items." (emphasis added)
Pulvermüller, F. (2003).
The neuroscience of language: on brain circuits of words and serial order. Cambridge University Press.
"lexical concepts do not arise in language use. Rather, they are units of linguistic knowledge abstracted from across usage events (i.e., utterances) that encode linguistic content and facilitate access to conceptual (i.e., non-linguistic) knowledge. Thus, a lexical concept is a unit of linguistic knowledge that populates the "mental grammar," deriving from commonalities in patterns of language use."
Evans, V. (2009).
How words mean: Lexical concepts, cognitive models, and meaning construction. Oxford University Press.
"it is almost universally assumed that concepts play a pivotal role in linguistic communication. According to the standard picture, people understand each others words in virtue of the fact that they associate the same (or quite nearly the same) concepts with those words. If no two people associate the same concepts with their words, then communication is impossible. Therefore, concepts must be sharable."
Prinz, J. J. (2004).
Furnishing the mind: Concepts and their perceptual basis. The MIT Press.
When we're describing a third person, the person being described doesn't need to conceive of the concepts being used to describe him
That's true. However, this only matters if the term does not necessitate a self-description to be held at least in theory. If an atheist really "lacks any belief" in god or gods the way a baby does, then they would be unable to use the word the way that everyone in this thread has. See above.
When I say "Brian is an atheist", it's not Brian who's using the word "atheist"; it's me.
Thank you for explaining the third person. If I said you were a
demioergos, it would be me using the word. It doesn't make it accurate