One who or that which flaps. / (hunting) A young game bird just able to fly, particularly a wild duck. / A flipper; a limb of a turtle, which functions as a flipper or paddle when swimming.

(colloquial, historical) A young girl usually between the ages of 15 and 18, especially one not "out" socially.

plural of flapper

The behaviour of flappers (young women).

A European skate, Dipturus intermedius, a subspecies of the common skate.

a fire beater

(historical) A mechanical display board, used at railway stations etc., having the text characters on individual flaps that can be rotated to form different messages.

plural of flapper board

plural of flapper valve

A kind of valve used in toilets, water softeners, etc. to create a watertight seal in the tank that holds water until it needs to be flushed, at which point the valve is raised.