If you've ever seen a space shuttle launch, you probably remember seeing all the white smoke billowing, or swelling and rolling forth, underneath.

You'll most often see the word billowing when someone is talking about smoke, steam, or the wind blowing through something, like hair or a flag. The word bylgja, from which billow derives, comes from an unusual source for English words: Old Norse.

Definitions of billowing

adj characterized by great swelling waves or surges

“the restless billowing sea”
billowy, surging
(especially of weather) affected or characterized by storms or commotion