Lappet \Lap"pet\, n. [Dim. of lap a fold.] A small decorative fold or flap, esp, of lace or muslin, in a garment or headdress. --Swift. {Lappet moth} (Zo["o]l.), one of several species of bombycid moths, which have stout, hairy caterpillars, flat beneath. Two common American species ({Gastropacha Americana}, and {Tolype velleda}) feed upon the apple tree.