To swoop means to move downward through the air in a smooth, curved path, usually quickly and with purpose. When a hawk swoops down from the sky to catch a mouse, it dives in one fluid motion. When your mom swoops in to catch a glass before it falls off the table, she moves swiftly with that same curved, purposeful motion.

Birds of prey are famous for their swooping. An eagle might circle high above a lake, then suddenly swoop down to snatch a fish from the water. The word captures both the speed and the graceful arc of the movement.

People also use swoop to describe sudden arrivals or quick actions. If your older sister swoops into your room and grabs the last cookie, she moved fast and caught you by surprise. When a teacher swoops by your desk to check your work, there's that same sense of quick, purposeful movement.

As a noun, a swoop is the movement itself: the swoop of a bird diving toward the ground.

The phrase “in one fell swoop” means doing something all at once, in a single action. If you clean your entire room in one fell swoop, you tackle everything at once instead of doing a little bit each day.