unthinking adj. + Add to list US //ənˈθɪŋkɪŋ// UK //ʌnθˈɪŋkɪŋ// un·think·ing SynonymsAntonymsEtymology Synonyms lumpenlumpishthoughtlessthoughtlesslyuncaringunreflectiveunthinkinglyunthoughtful Antonyms thoughtfullyOrigin From un- + thinking.