Free Dictionary vs Lingua Robot

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.

Lingua Robot is a RapidAPI-hosted REST dictionary covering more than 800,000 English lexical entries — words, phrasal verbs, and multiword expressions — with definitions, pronunciations, and morpheme/lemma data returned as JSON, documented on a separate Apiary reference site rather than its own marketing homepage. A live unauthenticated request against its real RapidAPI proxy host returned a reflected `access-control-allow-origin` header plus `access-control-allow-credentials: true`, reconfirming CORS; its free Basic tier covers 2,500 requests/day (then $0.004 each), with paid Pro/Ultra/Mega plans ($10-$99/month) raising the daily ceiling.