Reminiscent of a flapper (unconventional young woman of the 1920s).

present participle of flapdoodle

simple past tense and past participle of flapdoodle

(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.

(US) flapjack; pancake

plural of flapper skate