Is there a good machine-readable thesaurus that's free to download and use? We need to be able to canonicalise input into our app so that if we already have a record for 'what time is dinner' and the user adds 'when is dinner' we don't get a new record.
Hunspell includes a thesaurus library called MyThes. You can use that (or just the data files if you want to roll your own). If you're using .NET you can use NHunspell which is the same as Hunspell but for .NET. You should be able to get some good use out of that.