[plas.tron] n [MF, fr. OIt piastrone, aug. of piastra thin metal plate--more at piastre] (ca. 1507) 1 a: a metal breastplate formerly worn under the hauberk b: a quilted pad worn in fencing practice to protect the chest, waist, and the side on which the weapon is held
2: the ventral part of the shell of a tortoise or turtle consisting typically of nine symmetrically placed bones overlaid by horny plates 3 a: a trimming like a bib for a woman's dress b: dickey 1a
4: a thin film of air held by water-repellent hairs of some aquatic insects