rigid (adj.)youdaoicibaDictYouDict[rigid 词源字典]
early 15c., from Latin rigidus "hard, stiff, rough, severe," from rigere "be stiff," from PIE *reig- "stretch (tight), bind tightly, make fast" (cognates: Old Irish riag "torture," Middle High German ric "band, string"). Related: Rigidly.[rigid etymology, rigid origin, 英语词源]