WordNet is a lexical database for the English language.

CiteSeer is an excellent site for finding scholarly papers on this sort of thing. Look for papers on ontology.

If you limit your problem to a little world, you can do a very nice job and only miss awkward phrases. I would be interested to know how much effort is required to scale up a small world, and whether tools like WordNet can be leveraged to reduce this effort.

Don't be discouraged by a lack of reported successes in this area. Much of the work is outside of public view.