Superlative form of 'flappy'; most inclined to flap or most characterized by flapping motion; the extreme degree of being flappy.
From 'flappy' plus the superlative suffix '-est.' This creates the highest degree of the quality, following the same English pattern used in 'happiest,' 'fastest,' and other single-syllable adjectives.
The progression flappy → flappier → flappiest shows how English handles word comparison with a beautifully simple system that speakers add to new words instinctively, even ones invented recently.
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