1. A method, comprising: generating a dictionary comprising (a) one or more transformations of words from singular to plural form and (b) one or more transformations of words from plural to singular form; computing a probability, comprising a frequency of the transformation of a certain word occurring in a set of web documents relative to a frequency of the certain word occurring in the set of web documents; removing, from the dictionary, the certain word and the transformation if the probability is below a particular value; receiving a particular query from a user comprising a plurality of words; based on the particular query, determining whether a particular word in the particular query occurs in the dictionary; selecting from the dictionary a transformation of the particular word; and generating results based on executing a version of the particular query that includes both the particular word and the transformation of the particular word.