Gasket \Gas"ket\, n. [Cf. F. garcette, It. gaschetta, Sp. cajeta caburn, garceta reef point.] 1. (Naut.) A line or band used to lash a furled sail securely. {Sea gaskets} are common lines; {harbor gaskets} are plaited and decorated lines or bands. Called also {casket}. 2. (Mech.) (a) The plaited hemp used for packing a piston, as of the steam engine and its pumps. (b) Any ring or washer of packing.