Origin: 1250–1300; (adj.) Middle English souple flexible, compliant < Old French: soft, yielding, lithe < Latin supplic- (stem of supplex) submissive, suppliant, equivalent to sup-sup- + -plic-, variously explained as akin to plicāre to fold1, bend (thus meaning “bent over”; compare complex), or to plācāre to placate (thus meaning “in the attitude of a suppliant”); (v.) Middle English supplen to soften, derivative of the noun (compare Old French asoplir)
c.1300, from O.Fr. souple "pliant, flexible," from Gallo-Romance *supples, from L. supplex (gen. supplicis) "submissive, humbly begging," lit. "bending, kneeling down," thought to be an altered form of *supplacos "humbly pleading, appeasing," from sub "under" + placare "appease" (see placate).