Definition of billow verb from the Oxford Advanced American Dictionary
billow
verb
/ˈbɪloʊ/
1[intransitive] (of a sail, skirt, etc.) to fill with air and swell outThe curtains billowed in the breeze.2[intransitive]if smoke, cloud, etc.billows, it rises and moves in a large massA huge cloud of smoke billowed out of the chimney.