n. 1 a a fencer's leather-covered breastplate. b a lancer's breast-covering of facings-cloth. 2 a an ornamental front on a woman's bodice. b a man's starched shirt-front. 3 a the ventral part of the shell of a tortoise or turtle. b the corresponding part in other animals. 4 hist. a steel breastplate. plastral adj.
[ F f. It. piastrone augment. of piastra breastplate, f. L emplastrum PLASTER ]