supinate (v.)

c. 1500, "lying on the back," from Latin supinus "bent backwards, thrown backwards, lying on the back," figuratively "inactive, indolent," from PIE *(s)up- (see sub-). The grammatical use for "Latin verbal noun formed from the past participle stem" (mid-15c.) is from Late Latin supinum verbum "supine verb," perhaps so called because, though furnished with a noun case ending, it "falls back" on the verb. Related: Supinely.

"act of lying or state of being laid on the back," in anatomy, the movement of the forearm and hand which brings the palm of the hand uppermost (opposite of pronation); 1660s, from Late Latin supinationem (nominative supinatio), noun of action from past-participle stem of supinare "bend or lay backward or on the back" (see supinate).