Free Dictionary vs Synonyms

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.

The Synonyms API is STANDS4 Network's word-lookup service, returning synonym, antonym, and part-of-speech data for a submitted word as either JSON or XML from a single GET request against stands4.com's shared services endpoint — the same backend that powers sibling STANDS4 properties like Rhymes.com and Definitions.net. A live GET and OPTIONS preflight against that endpoint both echoed `access-control-allow-origin: *`; the service is free for up to 100 queries/day, with a paid commercial license available by contacting STANDS4 directly.