To make a series of quick delicate movements up and down or from side to side, or to cause something to do this. (Cambridge Dictionary)
To flap the winds rapidly. (Merriam – Webster)
To move with quick wavering or flapping motions. (Merriam – Webster)
To vibrate in irregular spasms. (Merriam – Webster)
(of a bird or other winged creature) fly unsteadily or hover by flapping the wings quickly and lightly. (Oxford Dictionaries)
If something thin or light flutters, or if you flutter it, it moves up and down or from side to side with a lot of quick, light movements. (Collins Dictionary)
If something light such as a small bird or a piece of paper flutters somewhere, it moves through the air with small quick movements. (Collins Dictionary)
Flutter. Your Dictionary.
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