I am digging through the old unanswered questions and periodically someone will be asking for a word that simply doesn't exist.
"There is no such word" is very much a valid answer to a single-word request. Not unlike how "no" is very much a valid answer to "is X grammatical in dialect Y?"
More to the point perhaps, "there is no such word" is a much better answer than "here's a random combo of letters I myself just sticked together". That is to say, we are not a site for coining neologisms.
And of course none of what I just said is a carte blanche for posting deliberately obscure single-word requests. The community is free to vote to close any and all questions that it deems to be over the top. Things like context, a sample sentence, the desired part of speech, and really just as many details as possible are never too much to ask for.
Say "there is no such word." Maybe suggest some things that are close, but point out why they don't exactly work. And most importantly, upvote the answers which say that there is no such word. We can't compel the OP to accept these answers, but we can make sure they get upvoted by the community.
In those cases, suggesting an alternative word or phrase that mostly fills the bill is better and more informative than just saying "I don't know" or "no such word exists". I don't know all English words, nor does anyone else on this site — but we, collectively, have an awesome vocabulary!
What you should do is answer with what you know, and someone with mastery of vocabulary can state faithfully that they are pretty sure there is no such word (if it is the case).
Of course, that is not often satisfying to people to state it so baldly. What is better is to elaborate, explaining possibly nearby words and their connotations (and how they are not sufficient for what is asked for), or if a neologism is offered how it sounds. Some suggestions may be rare, obsolete, technical, or dialectal which can be almost the same as 'does not exist'; that also calls for elaboration.
Then again, sometimes a request is just too specific: "Is there a word for how a dog's ear flops over when he turns his head trying to understand what you say?" (Oh please is there a word for that?). Sometimes there -are- words for such things, but then again sometimes there are not, so answer which way is the case.