Have you ever known what an idea was, but not known the exact word for it? You know the definition, but not the term, and someone tells you to look it up in the dictionary. That, of course, doesn’t work.
OneLook.com has a reasonable dictionary site of their own but that’s not really that interesting since you’ll find there’s an awful lot of online dictionaries if you start looking. This site also boasts a reverse dictionary. You plug in a rough definition of the word you want, and when you press the button it’ll spew out a slew of words that approximately match your definition. The better matches tend to appear closer to the top of the list, and the worse ones closer to the end.
This is one of those great applications that show the Internet can sometimes make life simpler. After all, can you imagine any way that a reverse dictionary would work without a computer? It’d be pretty difficult.