a. A projecting or hanging piece usually attached to something on one side and often intended to protect or cover: the flap of an envelope.
b. Either of the folded ends of a book jacket that fit inside the front and back covers.
c. A variable control surface on the trailing edge of an aircraft wing, used primarily to increase lift or drag.
d. Medicine A piece of tissue that has been partially detached and used in surgical grafting to fill an adjacent defect or cover the cut end of a bone after amputation.
a. The act of waving or fluttering: the flap of the flag in the wind.
b. The sound produced by this motion.
3. Linguistics A sound articulated by a single, quick touch of the tongue against the teeth or alveolar ridge, as (t) in water. Also called tap1.
4. Informal A commotion or disturbance: a flap in Congress over the defense budget.
5. Archaic A blow given with something flat; a slap.
v. flapped, flap·ping, flaps
1. To move (wings or arms, for example) up and down.
2. To cause to move or sway with a fluttering or waving motion: The wind is flapping the tent fly.
3. To cause to strike against something: flapped the paper on the table.
a. To move wings or the arms up and down.
b. To fly by beating the air with the wings: The crow flapped away.
2. To move or sway while fixed at one edge or corner; flutter: banners flapping in the breeze.
[Middle English flappe, slap.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.