Is there a way to match a string to natural language word?

I am toying with making a word game and was looking into some of the mechanics. I have run into a major roadblock though. I can’t find a way to match the word the player defines to an English word. Is there an API that I can query? I saw something on the asset store, but I am trying to keep everything free for this game. Any suggestions will help. The game will be HTML based so I could use a web API.

Thanks

The only way I could see doing this is with a dictionary. Just have a dictionary to match check if an input word is in it. You can find a dictionary online, and just do a search for if it contains the word in question.
A dictionary, as text is about 3mb I believe in size for all words.

Hope this helps.