Emily Dickinson Lexicon

FLAP, n. [G. lappen and klappe; D. lap or klap; Sw. klapp or lapp; Dan. klap or lap; Sax. læppa, a lap; W. llab, a stroke, a whipping; llabiaw, to slap; L. alapa, a slap. There is a numerous family of words in Lb, which spring from striking with something broad, or from a noun denoting something flat and broad. It seems difficult to separate flap from clap, slap, flabby, lap, &c.]

1. Any thing broad and limber that hangs loose, or is easily moved. A cartilaginous flap on the opening of the larynx. Brown. We say, the flap of a garment, the flap of the ear, the flap of a hat.
2. The motion of any thing broad and loose, or a stroke with it.
3. The flaps, a disease in the lips of horses. Farrier's Dict.