Other forms: billowing, billows, billowed
To billow is to swell and roll outward like smoke or a sail. Smoke billowed out, the curtains billow, billowing steam.
It is used most of smoke, cloth and cloud, where the movement is slow and rolling rather than sharp. As a noun a billow is a great wave, which is the original sense from Old Norse.
1verbbillowTo swell and roll outward like smoke or a sail.
“Black smoke billowed from the windows of the burning house.”
billow is a swelling.
Old Norse bylgja means a wave, with cognates across the Scandinavian languages.
Proto-Indo-European
*bʰelǵʰ-
Old Norse
bylgja
Middle English
*bilwe
English, today
billow
From Middle English bilwe, from Old Norse bylgja. From Middle English bilwe, borrowed from Old Norse bylgja, from Proto-Germanic bulgijō. Cognates include Danish bølge (“wave”); Norwegian Bokmål bølge (“wave”), Norwegian Nynorsk bylgje (“wave”); Swedish bölja (“wave”); German Low German Bulge, Bulg, Bülg (“billow, wave”); German Bulge (“billow, wave”). Compare bellow, bawl.
Etymology from Wiktionary, CC BY-SA