Below is a list of Free Online English Dictionaries:
THE FREE DICTIONARY BY FARLEX http://www.thefreedictionary.com/
The world’s most comprehensive dictionary: English, Spanish, German, French, Italian, Chinese, Portuguese, Dutch, Norwegian, Greek, Arabic, Polish, Turkish, Russian, Medical, Legal, and Financial Dictionaries, Thesaurus, Acronyms and Abbreviations, Idioms, Encyclopedia, a Literature Reference Library, and a Search Engine all in one!
OXFORD DICTIONARIES ONLINE http://oxforddictionaries.com/
a free site offering a comprehensive dictionary, grammar guidance, puzzles and games, and a language blog.
MACMILLAN DICTIONARY ONLINE http://www.macmillandictionary.com
The free online dictionary of Macmillan. Updated regularly and includes a thesaurus, fully integrated into the entries.
CAMBRIDGE DICTIONARIES ONLINE http://dictionary.cambridge.org/
Cambridge University Press has been publishing dictionaries for learners of English since 1995. Cambridge Dictionaries Online has been offering these dictionaries completely free of charge since 1999.
COLLINS DICTIONARY ONLINE http://www.collinsdictionary.com/