12. The system of claim 10 , wherein evaluating the synonym and the query term using one or more predetermined criteria includes determining whether the synonym and the query term are morphological variants.
10. A system comprising: one or more computers; and a computer-readable storage device having stored thereon instructions that, when executed by the one or more computers, cause the one or more computers to perform operations comprising: receiving a search query including a query term; obtaining a synonym that a synonym rule identifies as a substitute for the query term: evaluating the synonym and the query term using one or more predetermined criteria; and based on evaluating the synonym and the query term using the one or more predetermined criteria, designating the synonym as a restricted-locality synonym, wherein an occurrence, in a document that is identified as responsive to a search query, of a synonym that is designated as a restricted-locality synonym is scored according to a first scoring model, and wherein an occurrence, in a document that is identified as responsive to a search query, of a synonym that is not designated as a restricted-locality synonym is scored according to a second scoring model that is different than the first scoring model.