plastron

Etymology

Borrowed from French plastron, from Italian piastrone, augmentive of piastra (“breastplate”), from Latin emplastrum (“plaster”), from Ancient Greek ἔμπλαστρον (émplastron), from ἔμπλαστος (émplastos, “daubed, plastered”), from ἔμπλασσειν (émplassein, “to mould, form”).

noun

1. The nearly flat part of the shell structure of a tortoise or other animal, similar in composition to the carapace.
2. (fencing) A half-jacket worn under the jacket for padding or for safety.
3. A man's shirt-bosom.
4. An ornamental front panel on a woman's bodice.
   I bought here a wedding dress perhaps twenty or thirty years old … a sequin plastron to be worn over the womb as a feminine equivalent to a cod-piece, and a gauze veil embroidered in purple and gold. 1942, Rebecca West, Black Lamb and Grey Falcon, Canongate, published 2006, page 784
5. A breastplate.
   "Why, compared to what thou wast, Hugo, thou art as a deerskin coat to a steel plastron.-- Art thou not in love, man? Answer me!" "Something like, I fear me, beau sire,” replied the squire. 1831, George Payne Rainsford James, Philip Augustus, Or, The Brothers in Arms, page 122
   He therefore persuaded the Casa de Antillas to supply him with a hundred steel plastrons or corselets, with armlets and shoulder plates, and a hundred morions, or pikemen's helmets. This heavy armor was suitable […] 1964, Charles McKew Parr, Ferdinand Magellan, Circumnavigator, New York: T.Y. Crowell Company
6. A film of air trapped by specialized hairs against the body of an aquatic insect, and which acts as an external gill.
   The plastron of a diving beetle is not directly a source of oxygen, but acts as a gill, acquiring oxygen from the surrounding water.
   Total independence of atmospheric air is possible only if insects have a permanent gas store or incompressible gas gill, called a plastron. Unlike compressible gas stores, the volume of a plastron remains constant and it is incompressible. 2013, Jill Lancaster, Barbara J. Downes, Aquatic Entomology, page 45
   2013, Jon F. Harrison, Lutz T. Wasserthal (revisions & updates), 17: Gaseous Exchange, R. F. Chapman, Stephen J. Simpson (editor), Angela E. Douglas (editor), The Insects: Structure and Function, 5th Edition, page 535, The plastrons of other insects are generally less efficient than that of Aphelocheirus as they have a less dense hair pile from which the air is more readily displaced.