[QUOTE=begbert2]
You’re correct that the archaic definitions are outdated - so much so, in fact, that they’re irrelevent to the discussion. The only two meanings of the word that matter are its modern meaning, and the meaning it had in Einstein’s time (to make sure we interpret his statements about it correctly).
The question of whether Buddha counts as a god (or rather, whether any specific version and state of Buddha counts as a god) is relevent to the question of whether believing in Buddha disqualifies you from the atheist label - and it’s something I’m not qualified to answer, which my ignorance of Buddhism in general. However I don’t believe in any supernatural or abnormal incarnation of any Buddha, so I’m still good regardless. 
I think that using words in ways that are inconsistent with their common meaning is not useful at all. If you don’t like the meaning of the word ‘atheism’, don’t use the word. Heck, I don’t even think this is a good “extension of meaning”, since it doesn’t add anything constructive - it just modifies the set of things disbelieved in from one moderately clear set to an even less clearly defined set, which unlike the original has no relation whatsoever to the root or historical meanings of the word. Ick.
The language will evolve quickly enough without deliberate misuse - just use other words that actually mean what you want to say. When you do use “atheism”, use it only to refer to disbelief in gods, all gods, and only gods. Please.
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My point is that it can be awfully difficult to determine, in a non-Western context, what qualifies as a “god” for the purpose of disbelief and what doesn’t; as the Buddhist example demonstrates.
The issue with Buddhism is that, while it contains within it a purely non-theistic philosophy of personal liberation (no gods or supernatural elements are strictly necessary for the Four Noble Truths or following the Eightfold Path), some mainstream varieties of Buddhism early developed into religion in which buddha-figures are seen as presiding over heavens, and Arhats act much as saints do in Catholicism; and in which figures recognizable as priests tend to temples in which statues and relics are venerated, and incense burned.
According to some (see Diogenes above) Buddhism is still in essence “non-theistic”, and thus a Buddhist is an atheist. But this to my mind makes no sense. Person A goes forth to a temple, woships a giant seated idol of the Pure Land Buddha, burns incense, offers prayers in the hopes of gaining a happy afterlife - to call that person an “atheist” seems to me to stretch the meaning of the word to the breaking-point.
Now, I suppose some may argue that this isn’t the original concept of Buddhism; but it, or some variant of it, is the form of Buddhism that most actual Buddhists actually practice. Buddhists themselves traditionally have not been terribly concerned about the distinction between theism and atheism - early Buddhism accepted the existence of the Hindu gods no problem (just felt sorry for 'em as they were bound to the wheel of samsara). It wasn’t the sort of big wrench for Buddhists to accept Buddhas as essentially gods, as it would be for modern Westerners (who tend in consequence to be attracted to the more esoteric varieties of Buddhism such as Zen).
The point? That outside the easy dichotomies we are used to - philosophy/religion, or Abrahamic God/Atheism, the familiar categories of label aren’t terribly useful. The Einstein case is illustrative of this.