Definition of plastron
1a : a metal breastplate formerly worn under the hauberkb : a quilted pad worn in fencing 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
3a : a trimming like a bib for a woman's dressb : dickey 1a
4 : a thin film of air held by water-repellent hairs of some aquatic insects
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Did You Know?
English speakers first borrowed French's word for a breastplate, plastron, as the name for the protective plate worn under a tunic of [chain mail](/dictionary/chain mail) by knights. In the 17th century, plastron was extended to the pad used to protect the torso of a fencer. Two centuries later, herpetologists appropriated the word for a slightly different type of protection: the underside of a turtle's shell, which consists typically of nine bones overlaid by horny plates. That was followed by the word's application in the world of fashion to coverings that adorn the front of a woman's bodice, such as a lacy bib, as well as to a man's separate or detachable starched shirtfront (which is typically worn under a jacket).
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Britannica.com: Encyclopedia article about plastron
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