supine. adj. 1. lying or resting on the back with the face, palm, etc, upwards. 2. displaying no interest or animation; lethargic. n. 3. (Grammar) grammar a noun form derived from a verb in Latin, often used to express purpose with verbs of motion. Abbreviation: sup. [C15: from Latin supīnus related to sub under, up; (in grammatical sense) from Latin verbum supīnum supine word (the reason for this use is unknown)]. (adj. suˈpaɪn; n.