IPA: /ˈflæpiər/
KK: /ˈflæpi/
Having more movement or looseness than something else that is flappy.
The bird's wings were flappier than those of the other birds in the flock.
Comparative: flappier
Superlative: flappiest
Flappier → It is formed from "flap" (of uncertain origin, possibly imitative of the sound made) and the suffix "-ier" (meaning more). The word "flappier" means more flappy or having a greater tendency to flap.
Think of something that is 'more flappy' — the root 'flap' suggests a movement that is light and quick, and the '-ier' indicates an increase in that quality.