Definition of billow cloud
: a long narrow cloud or usually a series of such clouds roughly parallel to each other caused by the flow of one layer of air over another producing waves at their interface the relatively cold crests of which are cloud-capped and their relatively warm troughs clear when the humidity is just right
Test Your Vocabulary
Commonly Confused Words Quiz
-
- I went to the ______ store to buy a birthday card.

Test your knowledge - and maybe learn something along the way.
TAKE THE QUIZ
A daily challenge for crossword fanatics.
TAKE THE QUIZLove words? Need even more definitions?
Merriam-Webster unabridged
Share billow cloud