IPA: /ˈflæpiəst/
KK: /ˈflæpiɪst/
The most loose or fluttering, often used to describe something that moves or hangs loosely in the air.
The flappiest flag waved proudly in the wind.
Comparative: flappier
Superlative: flappiest
Flappiest → It is formed from "flappy" (an adjective meaning characterized by flapping, likely derived from the verb "flap" which comes from Middle English "flappen", meaning to strike or move with a quick motion) and the suffix "-iest" (meaning most). The word "flappiest" describes something that has the most flapping motion or characteristics.
Think of something that is 'characterized by flapping' ('flappy') and remember that 'flappiest' means having the most flapping motion.