Whether English is your native language or not, there will be a time you don't know a particular word is but you know the Concept. I myself have experienced it so many times and it's very frustrating.

Here is a good "Reverse Dictionary" site called OneLook. You just need to type the concept with a few keywords. Then it will show you a list of possible words you're looking for. For example, let's say you forgot the word for "monkey bars" but you know that it's a bar kids climb in playground. So type something like "kids playground climb bar". Bingo!!! You'll see "Monkey Bars".