Are there any websites, search engines, etc. that can help you find the word you are looking to use?

You know for when you are writing and there is this one incredible word or phrase that you know you know, but you just can't completely grasp. Something that I could enter in a couple synonyms and maybe a few letters, i.e. the prefix or suffix. and be given multiple options. I know this sounds a lot like a thesaurus want ad, but really it's slightly different.