1. A computer-implemented method comprising: identifying a plurality of documents having one or more questions and, for each question, a corresponding answer; generating a plurality of question-answer pairs from the questions and respective corresponding answers occurring in the plurality of documents; training a statistical machine translation model using the plurality of question-answer pairs, including using each question of each question-answer pair as a source language input and a corresponding answer of the question-answer pair as a target language input, wherein each question and each corresponding answer are in the same natural language; translating, using the statistical machine translation model trained on the plurality of question-answer pairs, a phrase into one or more corresponding translated phrases; and determining one or more synonym pairs by comparing the phrase with the one or more corresponding translated phrases.