- billow (n.)
- 1550s, perhaps older in dialectal use, from Old Norse bylgja "a wave, a billow," from Proto-Germanic *bulgjan (source also of Middle High German bulge "billow, bag"), from PIE *bhelgh- "to swell" (see belly (n.)).
- billow (v.)
- 1590s, from billow (n.). Related: Billowed; billowing.
