Our English Librarian recommends the OED as the best dictionary for English Undergraduates
Why?
You can use it as a standard dictionary, but also, alongside 'present day' meanings, the OED can tell you about the history and usage of the particular word you are looking up.
Cambridge Dictionary: A mixture of free and subscription resources. Various language dictionaries are freely available.
Collins dictionary: Free online resource. Includes dictionaries for Enfgish or bilingual word reference for various languages plus thesauri.
Dictionary.com: Free online dictionary. Thesaurus also available as well as a free mobile app. The Random House unabridged dictionary is the foundation of this resource.
Merriam-Webster dictionary online: Free access to longstanding US dictionary and thesaurus service
University of Exeter LibGuide is licensed under CC BY 4.0