Many websites offer free dictionaries, including Wiktionary, The Free Dictionary and Merriam-Webster. These websites allow users to see the definitions of most words in the English language.
Wiktionary is a free online dictionary that claims to archive English definitions for over 4 million words from 1550 languages. Wiktionary's stated goal is to use English definitions to describe all words of all languages. Users can browse the definitions of millions of words by either searching for a specific word or by browsing alphabetized archives of Wiktionary's entries. The Free Dictionary is a free online directory of language resources, and includes extensive dictionaries in over a dozen languages.