1. a small whale with a rounded snout and triangular dorsal fin

1. to move up and down like a porpoise swimming
Usage: informal

Examples

• A pod of porpoises swam alongside our boat.
• The harbor porpoise is common in these waters.
• We watched the porpoises leap out of the water.
• The motorcycle began to porpoise over the bumpy road.
• The small plane started to porpoise during landing.
• Porpoises are often confused with dolphins by casual observers.