Here you have a list of dictionaries that we will update frequently.
Wordreference, Assorted Monolingual and Bilingual Dictionaries and links to other Dictionaries.
Merriam-Webster Online, Dictionary, Thesaurus, Medical Dictionary and Spanish-English Dictionary
Cambridge Dictionary, Dictionary, Idioms and Phrasal Verbs
Collins Dictionary, Monolingual and Bilingual Dictionaries
Photographic Dictionary, visual dictionary, good for basic students
The Free Dictionary, Dictionary, Encyclopedia and Thesaurus. Legal Dictionary, Medical Dictionary, Dictionaries in other Languages.
Linguee, Dictionary created by internet users with real examples of words in context.
Forvo, Pronunciation Dictionary where words are pronounced by native speakers.
Wordhippo, Find meanings, antonyms, synonyms, related words, rhyming words, plurals, pronunciation, meaning of names, etc.