peritoneumn.

Etymology: < post-classical Latin peritoneum membrane which lines the inside of the abdominal cavity (4th cent.; also as peritonaeum , peritoneon , peritonium ; earlier in classical Latin as peritonaeos ), perineum (1312 or earlier, also as misreading in manuscripts of 5th and 6th-cent. authors for perineum , perineos (see perineum n., and note below) < ancient Greek περιτόναιον , use as noun of neuter of Hellenistic Greek περιτόναιος stretched over (adjective) < περίτονος stretched over ( < ancient Greek περι- peri- prefix + τόνος tone n.) + -αιος, suffix forming adjectives. Compare Middle French peritoneon, peritoneum perineum, peritoneum (1314), Middle French, French peritoine peritoneum (1520), Italian peritoneo (1574; earlier as peritoneum (a1493)).In form peritonei after the Latin genitive ending. In form peritonius after Latin masculine ending (compare classical Latin peritonaeos , masculine). In form peritone perhaps after Middle French peritoine (although this is apparently first attested later). Confusion between post-classical Latin peritoneum and perineum , perineos perineum n. apparently set in at a very early date and led to the use of peritoneum in the sense ‘perineum’ in medieval sources. The translation which is cited in quot. ?a1425 at sense 2 as using perytoneon in this sense is De iuvamentis membrorum, a post-classical Latin translation (probably a1300) of an Arabic abbreviated version of Galen's De utilitate partium.