/ ˈbɪləʊ; NAmE -loʊ/ verb , noun
■ verb [ v ]
1.
( of a sail, skirt, etc. ) to fill with air and swell out :
The curtains billowed in the breeze.
2.
if smoke, cloud, etc. billows , it rises and moves in a large mass :
A great cloud of smoke billowed out of the chimney.
■ noun
[ usually pl. ] a moving mass or cloud of smoke, steam, etc. like a wave
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WORD ORIGIN
mid 16th cent.: from Old Norse bylgja .