Full disclosure up front: I personally "live" in that tag. It's one of the tags I have marked as favorite, and it's one of the tags I have used to "promote" our site by creating this tag set over at StackExchange, which has brought quite a lot of traffic our way on quite a few occasions, and seems to be rather popular in general (it's still on page 2 after all this time).
I totally see how this tag can be regarded as meta. However, I don't think that it is any more meta than word-choice. And it's actually more useful than certain non-meta-tags. The tag nouns doesn't tell you anything about the content of a question and it doesn't tell you anything about what “kind” of question it is. (Is it about usage? spelling? etymology? pronunciation?) With the tag single-word-request, you at least know the latter. In fact, this tag is exceptionally clearly defined, it tells you everything about the question except for what word the OP is actually looking for, but that's why he's asking the question in the first place. I don't recall anyone ever using it by mistake.
In short: I vote to keep it, but I will live with any decision the community takes on this.
Edit: Also, I think we should pause for a second and ask ourselves, why do we have tags in the first place? What purpose do they serve? They are not just decoration. They are there for navigation. They are there so that questions can be sorted into meaningful categories, which can then be easily browsed, followed, or ignored. I just can't imagine anyone following nouns and ignoring verbs, or vice versa. But I know of at least one person (myself) who follows the single-word-requests; I see that at least two other people follow the aforementioned tag set on StackExchange, which includes single-user-requests (and word-choice); and I know of at least one user who has recently commented here on meta that he doesn't care about this type of questions, and would rather ignore them. The tag is clearly doing more good than harm.
Edit 2, in response to comments: yes, I am convinced that single-word-request can work as the only tag on a question. I have seen it do just that. And in fact, if it were deleted, then what else would you tag these questions with? In that regard, it is no different than etymology or pronunciation. Here, let's just break down what questions we have on this site:
- if your question is about etymology, then it's, well, etymology
- if it's about dialects, it's dialects
- if it's about, dare I say it, grammaticality, that's grammaticality (I hope we have settled on that one)
- if you don't know how to spell a word, that's spelling
- if you're not sure how to pronounce it, that's pronunciation
- if you have two (or more) words and are not sure which one to use, that's word-choice
- if you are not sure where a word goes in a sentence, that's word-order
- if you have a word and are not sure about its meaning, that's meaning
- and if you have the meaning but don't know how to express it in a single word, then it's, umm, what? nouns? Well, sure, sometimes it is, but in any case, part-of-speech tags are secondary, additional, completely orthogonal tags that could be applied to all of the above questions as well. In fact, it's the POS tags that won't work on their own — and note how nobody takes that to mean that they are somehow "meta".
single-word-request can, and does, work as the only tag on the question. Sometimes you are not sure if you're looking for an adjective, an adverb, a participle, or a noun. You just have that vague idea floating in your head, and you want to pack it into a single word, and then build a sentence around that word accordingly, be it a noun or a verb. If that tag got deleted, people would (have to) resort to tagging their questions with something less appropriate, such as writing, which would water down that tag, or english, or fun, or some other nonsense. Or they will just keep re-inventing single-word-requests as looking-for-a-word or something. Now that would do more harm than good.