bobber

This term is primarily used within the specialized context of angling. It describes a functional tool designed for visual signaling, where the physical action of sinking or vibrating alerts the fisher to a strike. In this technical sense, it is a synonym for a float, though "bobber" is more common in North American English.

Outside of fishing, the word serves as a descriptive noun for any object characterized by rhythmic vertical motion in a fluid. This usage is more literal and less technical, focusing on the physical behavior of buoyancy and oscillation rather than a specific piece of equipment.