Definitions of billow:

• noun:   a large sea wave
• verb:   rise and move, as in waves or billows
• verb:   rise up as if in waves

  Example: "Smoke billowed up nto the sky"

• verb:   move with great difficulty

  Example: "The soldiers billowed across the muddy riverbed"

• verb:   become inflated
• name:  A surname (very rare: popularity rank in the U.S.: #65604)