Free Dictionary vs Wordnik

Free Dictionary API is a keyless REST service built and maintained by a solo developer, returning English word definitions, phonetic spellings, audio pronunciation clips, parts of speech, usage examples, and synonyms/antonyms as plain JSON from a single GET request. It now serves more than 10 million requests a month and is funded entirely through voluntary donations rather than any paid tier.

Wordnik's REST API returns word definitions aggregated from multiple published dictionaries alongside example sentences, pronunciations, related words, and corpus-derived frequency data, documented through an interactive Swagger UI. Every developer gets a free Basic plan (100 calls/hour, with an explicit nonprofit/research allowance) before paid Hobby, Pro, and Enterprise tiers raise the ceiling up to 45,000 calls/hour -- revenue that funds Wordnik's nonprofit mission to document the English language.