Pronunciation (UK) (US) IPA (key): /ˈræpɪd/ Audio (US)(file) Adjective Positive rapid Comparative rapider Superlative rapidest If an action or idea is rapid, it happens quickly. Synonyms: fast and quick Related words rapidity rapidly rapidness Noun Singular rapid Plural rapids (usually plural) A fast part of a river or stream.Wikiwand - on Seamless Wikipedia browsing. On steroids.Remove ads