It is not a sweeping guideline, or the FAQ would report that single-word requests are questions that should not be asked.
It must be decided on a case-by-case basis, making some considerations, such as:
- Does the question describe exactly in which context the OP wants to use a single word?
- Does the question report exactly the criteria for which the suggested word will be accepted?
- Does the question report which words the OP didn't like?
- Does the question shows the OP searched for a suiting word, before asking the question?
Grammatically, there is nothing wrong in using two or more words instead of a single word; if the OP needs to really use a single word, then the OP should exactly describe in which context the word is being used, otherwise the answer is going to be too generic to be useful, to who asks the question, and for the future readers, who could wrongly understand that the word suggested in the accepted answer is always the better word to use.
The reason to know which words the OP possibly thought of, but didn't like, is avoiding that who answers gets "I have thought of this, but I didn't like it" as answer. If who answer know which words the OP already thought of, they will avoid suggesting those words.
It is quite annoying suggesting a word, and being said the OP doesn't like it. That is the reason the OP should report the exact criteria that will be used to accept the suggested word. Listing those criteria is useful, IMO, otherwise it seems the OP is accepting the word he likes more, which is a rather subjective method to accept an answer, which makes the question itself not useful for future readers, and rather subjective.
Showing to have searched for a word before to ask the question is useful for this kind of questions, as they could seem to be asked because the OP could not be bothered to search himself.