prolong (v.)youdaoicibaDictYouDict[prolong 词源字典]
early 15c., back-formation from prolongation or else from Old French prolonguer, porloignier (13c.), from Late Latin prolongare "to prolong, extend," from Latin pro- "forth" (see pro-) + longus "long" (adj.); see long (adj.). Related: Prolonged; prolonging; prolongable.[prolong etymology, prolong origin, 英语词源]