At present we have several tags for specific words, such as [while], [that], and others. IMHO this practice should be strongly discouraged, lest the tag list just become an English dictionary. Questions about usage of particular words should be tagged with the kind of word in question, e.g. [conjunction], [adjective], etc.
I agree with this as a general principle, but I think that there are probably going to be some words that get asked about a lot that it may be sensible to make them their own tags. There are no such words yet that have even two questions with the same tag, so I don't think there are any candidates for the special treatment yet. I do support this as a general rule though, to appear in the FAQ, or wherever.
What questions might be asked on the same words that wouldn't (in theory, at least) be closed as duplicates? Sure, there will likely be the occasional additional question on the same word, but not enough to warrant tagging. I agree that word tagging is unnecessary.