Etymology: In sense 1 < (i) Middle French supin, suppin (first half of the 13th cent. in Old French; French supin ), and its etymon (ii) post-classical Latin supinum gerund, supine (3rd cent.), use as noun (short for supinum verbum supine verb) of neuter singular of classical Latin supīnus (see supine adj.), in post-classical Latin also (in grammar) passive (5th cent. in an isolated attestation). In sense 2 < supine adj.With sense 1 compare Spanish supino (1490). With sense 1b compare also German Supinum (second half of the 17th cent. or earlier; 1735 or earlier with reference to German, 1777 or earlier with reference to English). Post-classical Latin supinum was also used to denote ‘neuter’ verbs (see neuter adj. 1b), i.e. verbs with active inflection and passive sense. The reason for the grammatical use is not clear. Some scholars compare ancient Greek ὕπτιος ‘lying on one's back, upturned’, used by the Stoics to designate the passive voice, and argue that the Latin grammatical use of supīnus was modelled on this, as several of the forms or categories concerned are associated with the passive. Others argue that Greek is not relevant as the grammatical categories in question are not found in Greek, and that the use may arise from the fact that gerunds and supines are indifferent to person, number, tense, and voice.

Etymology: < classical Latin supīnus lying face upwards, flat on one's back, (of the hands ) turned palm upwards, (of the head or face) upturned, thrown back, (of terrain) flat, low-lying, sloping down, (of people) passive, sluggish < the stem of super above (see super- prefix) and superus higher (see superior adj.) + -īnus -ine suffix¹. Compare Old French sovin (11th cent. in Rashi; Middle French souvin), Anglo-Norman and Middle French supin, Middle French suppin (early 13th cent.), Old Occitan sobin, sopin (11th cent.), Catalan supí, Spanish supino (16th cent.), Portuguese supino (14th cent. as sobinho), Italian supino (early 14th cent.). N.E.D. (1917) gives the pronunciation as (sⁱūpəi·n) /s(j)uːˈpaɪn/, occasionally (sⁱū·pəin) /ˈs(j)uːpaɪn/. In British English, pronunciation with stress on the first syllable became usual during the first half of the 20th cent.; in U.S. English, stress on the second remains more usual.