Reverse dictionary may be the answer. I think it's something every writer shouldn't be without.
OneLook's reverse dictionary lets you describe a concept and get back a list of words and phrases related to that concept. Your description can be a few words, a sentence, a question, or even just a single word.
It's not perfect but it's a good first step towards finding that word. Of course the tried and true method of going through thesaurus listings is always helpful.