plastron

noun6

1. •
   A half-jacket worn under the jacket for padding or for safety.
2. •
   The nearly flat part of the shell structure of a tortoise or other animal, similar in composition to the carapace.
3. •
   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
4. •
   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.
5. •
   A man's shirt-bosom.
6. •
   An ornamental front panel on a woman's bodice.