Plastron

//ˈplæstɹən// noun

noun ·Uncommon ·Advanced level

Definitions

Noun
  1. 1
    The nearly flat part of the shell structure of a tortoise or other animal, similar in composition to the carapace.

    "The great tortoise that in myth is said to support the world and is thus an embodiment of the galaxy, without whose swirling order we would be a lonely wanderer in space, is supposed to have revealed in ancient times the Universal Rule, since lost, by which one might always be sure of acting rightly. Its carapace represented the bowl of heaven, its plastron the plains of all the worlds."

  2. 2
    (zoology) the part of a turtle's shell forming its underside wordnet
  3. 3
    A half-jacket worn under the jacket for padding or for safety.
  4. 4
    a large pad worn by a fencer to protect the chest wordnet
  5. 5
    A man's shirt-bosom.
Show 6 more definitions
  1. 6
    a metal breastplate that was worn under a coat of mail wordnet
  2. 7
    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."

  3. 8
    the front of man's dress shirt wordnet
  4. 9
    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."

  5. 10
    the ornamental front of a woman's bodice or shirt wordnet
  6. 11
    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."

Example

More examples

"A female tortoise has a flat 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”).

Related phrases

half jacket

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Data sourced from Wiktionary, WordNet, CMU, and other open linguistic databases. Updated March 2026.