flappy
adj. B2 Upper Intermediate flap·py
adj. describing something that moves in a loose or wobbly way, like a bird's wings. It can also describe a person who is acting in a silly or annoying way.
adj. characterised by loose, wobbly, or fluttering movement; also used to describe a person's manner as foolish or unsteady. Informal in register.
The flappy wings of the bird made a soft noise.
He had a flappy way of walking, as if he were trying to balance on a tightrope.
The flappy fabric of the tent caught the wind, causing the entire structure to sway dangerously in the high-altitude breeze.