A bobbing motion; a quick up and down movement.

“a bob of the head”

A curtsy.

A bobber (buoyant fishing device).

To move gently and vertically, in either a single motion or repeatedly up and down, at or near the surface of a body of water, or similar medium.

“The ball, which we had thought lost, suddenly bobbed up out of the water.”

To move (something) as though it were bobbing in water.

“I bobbed my head under water and saw the goldfish.”

To curtsy.