It doesn't matter what you're writing; it could be an essay for school or a book to be published. Chances are you have at one point thought of something you want to add, but you just cannot recall the word no matter how had you try. So you look it up, but it rarely ever gives you the word you feel is right. At this point, you might just give up, or you might write a few sentences explaining the one word.
Well I've found a website for you. 
OneLook Reverse Dictionary
It basically does exactly what it says and it is absolutely wonderful. It is a reverse dictionary: you put in the meaning and it gives you the word.

Your'e welcome.