sappy (adj.)youdaoicibaDictYouDict[sappy 词源字典]
"full of sap," Late Old English sæpig, from sæp (see sap (n.1)). Figurative sense of "foolishly sentimental" (1660s) may have developed from an intermediate sense of "wet, sodden" (late 15c.). Earlier, now obsolete, figurative senses were "full of vitality" (1550s) and "immature" (1620s).[sappy etymology, sappy origin, 英语词源]