One Look Reverse Dictionary is exactly that — a “reverse” dictionary. Here’s how the site describes itself:
“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. Just type it into the box above and hit the “Find words” button. Keep it short to get the best results. In most cases you’ll get back a list of related terms with the best matches shown first.”
It could possibly be useful to English Language Learners. However, I think the thesauruses in The Best Reference Websites For English Language Learners — 2008 work as well — if not better.
Thanks to the Make Use Of blog for the tip.