suckle (v.)youdaoicibaDictYouDict[suckle 词源字典]
c. 1400, perhaps a causative or frequentative form of Middle English suken "to suck" (see suck), but OED suggests instead a back-formation from suckling (though this word is attested only from mid-15c.). Related: Suckled; suckling.[suckle etymology, suckle origin, 英语词源]