ruinous (adj.)youdaoicibaDictYouDict[ruinous 词源字典]
late 14c., "going to ruin," from Old French ruinos (Modern French ruineux) or directly from Latin ruinosus "tumbling down, going to ruin," from ruina (see ruin (n.)). Meaning "causing ruin" is from mid-15c. Related: Ruinously.[ruinous etymology, ruinous origin, 英语词源]