Urban Dictionary is a crowdsourced online dictionary of slang words and phrases. It was founded in 1999 as a parody of Dictionary.com and Vocabulary.com by then-college freshman Aaron Peckham.

TheFreeDictionary.com, together with TheFreeLibrary.com, is the world's most comprehensive online database of reference information.

The web's most popular dictionaries for learners. Cambridge University Press has been publishing dictionaries for learners of English since 1995.

Oxford Advanced Learner's Dictionary is the largest and most trusted free online dictionary for learners of English. Quickly find clear definitions and audio pronunciations of words.

For more than 150 years, in print and now online, Merriam-Webster has been America's leading and most-trusted provider of language information.