Reference » Dictionaries

Longman English Dictionary - http://www.ldoceonline.com/

The leading dictionary for learners of English of all ages and levels who want to learn more about English: definition, idioms, examples and more.

Oxford English Dictionary (OED) - http://oed.com/

An unsurpassed guide to the meaning, history, and pronunciation of 600,000 words— past and present—from across the English-speaking world.