1. A computer-implemented method comprising: obtaining, at one or more computers, a pair of terms in a first language, the pair of terms being commonly co-occurring non-synonyms in a corpus of documents, the corpus of documents being in the first language; determining a set of variations for each term in the pair of terms; generating a set of known related input pairs based on the sets of variations for each term in the pair of terms; for each input pair of terms in the set of known related input pairs, translating, by an automatic translation system, each term in the pair of terms into a second language plurality of languages to generate a set of translated terms; adding, at the one or more computers, the set of translated terms to a blacklist of known non-synonym pairs for at least one of the plurality of languages; and determining, based on the blacklist of known non-synonym pairs, whether a pair of candidate terms in at least one of the plurality of languages are synonyms.