billow (n.)youdaoicibaDictYouDict[billow 词源字典]
1550s, perhaps older in dialectal use, from Old Norse bylgja "a wave, a billow," from Proto-Germanic *bulgjan (cognates: Middle High German bulge "billow, bag"), from PIE *bhelgh- "to swell" (see belly (n.)).[billow etymology, billow origin, 英语词源]
billow (v.)youdaoicibaDictYouDict
1590s, from billow (n.). Related: Billowed; billowing.