This problem is faced by me often when I search something on Web.
When we don't know meaning of a word, we just refer a dictionary and understand it but what if I know how to describe a thing but don't know what word do we denote it by?
Do we have a word to represent such "reverse search"?
Example: Let's say I don't know the word "witch" but I know that there exist something known as "a woman having evil power", how to search such things on the web so that we can get the word witch?