to spring forward or swoop down suddenly to seize something
(often + on) to act or react swiftly to take advantage of something, e.g. a mistake
to swoop on and seize something with talons or claws
(often + on) to seize something suddenly, eagerly, or with force
She pounced on his offer
to make a sudden attack or approach
[Middle English pounce talon, sting, prob by shortening and alteration from punson pointed tool, dagger, from early French poinçon: see puncheon2]