Dictionary entry overview: What does adamant mean? • ADAMANT (noun) The noun ADAMANT has 1 sense: 1. very hard native crystalline carbon valued as a gem Familiarity information: ADAMANT used as a noun is very rare. • ADAMANT (adjective) The adjective ADAMANT has 1 sense: 1. impervious to pleas, persuasion, requests, reason Familiarity information: ADAMANT used as an adjective is very rare.