22. The system of claim 17 , where the term is from a search query and the candidate synonym is not a valid synonym for the term, the system further programmed to perform operations comprising: determining, from an analysis of a number of terms in the search query, whether to perform one of expanding the search query to include the candidate synonym or ranking search results responsive to the search query using the candidate synonym instead of expanding the search query to include the candidate synonym.
23. The system of claim 22 , where the determination is further based on an estimated number of search results responsive to the search query.