Oxford English DictionaryThis link opens in a new windowWith 600,000 words, 3 million quotations; and over 1000 years of English, the Oxford English Dictionary (OED) is widely regarded as the accepted authority on the English language.
Merriam-WebsterThis dictionary provides not only definitions, but lists of synonyms and antonyms and information about the history and etymology of words.
Cambridge DictionaryEnglish-language dictionaries at multiple levels, as well as English/foreign language dictionaries.
LexicoPowered by Oxford, Lexico's Dictionary & Thesaurus offers trusted English definitions, synonyms, & grammar guides for native speakers & language learners.
Etymologies refer to the origin and history of development of words.
Google Books Ngram ViewerThe Google Books Ngram Viewer allows a user to trace the popularity of a word over time. Enter a phrase and retrieve a graph showing how those phrases have occurred in a corpus of books (e.g., "British English", "English Fiction", "French") over the selected years.
Online Etymology Dictionary"Etymologies are not definitions; they're explanations of what our words meant and how they sounded 600 or 2,000 years ago. The dates beside a word indicate the earliest year for which there is a surviving written record of that word (in English, unless otherwise indicated)."
Trends.google.comFind out how frequent a word has been searched on Google. Useful for the etymology of modern words or neologisms.