plastron

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A metal breastplate worn under a coat of mail.
2. n. A quilted pad worn by fencers to protect the torso and side.
3. n. A trimming on the front of a bodice.
4. n. The front of a man's dress shirt.
5. n. The front panel of the tunic of a uniform, usually of a different color than the rest.
6. n. Zoology The ventral part of the shell of a turtle or tortoise.

Century Dictionary and Cyclopedia

1. n. A breastplate; a garment or part of a garment covering the breast. , , , Specifically— The early breastplate worn under the hauberk or broigne: one of the earliest pieces of plate-armor introduced in the European middle ages. C. Boutell, Arms and Armour in England
2. n. In herpetology: The ventral part of the shell of a chelonian or testudinate; the lower shell, or under side of the shell, of a turtle or tortoise: more or less opposed to carapace. The plastron is wholly an exoskeletal or integumentary structure, in which no bones belonging to the endoskeleton or skeleton proper are found. It consists of a number, typically nine, of separate dermal bones, developed in membrane, and covered with horny epidermis, or tortoise-shell. The nine typical pieces are one median and four pairs lateral, called entoplastron, epiplastron, hyoplastron, hypoplastroan, and xiphiptastron. Formerly, when these were supposed to contain or represent sternal elements, they were respectively named entosternum epistemum, hyosternum, hypoternum, and xiphisternum. The plastron is usually immovable, like the carapace, but may be variously hinged, in some cases so as to shut the animal in completely. See also cuts under carapace, Pleurospondylia, and Chelonia.
3. n. One of the similar exoskeletal plates developed upon the under side of the body of certain Amphibia, as the Labyrinthodonta.
4. n. In mammalogy, the ventral shield or cuirass of the glyptodons or fossil armadillos.
5. n. In anatomy, the sternum with the costal cartilages attached, as removed in autopsies.
6. n. In ornithology, a colored area on the breast or belly of a bird, like or likened to a shield.
7. n. In the Echinodermata, a space surrounded by the subanal fasciole lying beneath the anus, in spatangoid echinoids.

Wiktionary

1. n. The nearly flat part of the shell structure of a tortoise or other animal, similar in composition to the carapace.
2. n. fencing A half-jacket worn under the jacket for padding or for safety.
3. n. An ornamental front panel on a woman's bodice.
4. n. A film of air trapped by specialized hairs against the body of an aquatic insect, and which acts as an external gill.

GNU Webster's 1913

1. n. A piece of leather stuffed or padded, worn by fencers to protect the breast.
2. n. (Anc. Armor) An iron breastplate, worn under the hauberk.
3. n. (Anat.) The ventral shield or shell of tortoises and turtles. See Testudinata.
4. n. A trimming for the front of a woman's dress, made of a different material, and narrowing from the shoulders to the waist.

WordNet 3.0

1. n. a metal breastplate that was worn under a coat of mail
2. n. a large pad worn by a fencer to protect the chest
3. n. the ornamental front of a woman's bodice or shirt
4. n. the front of man's dress shirt
5. n. (zoology) the part of a turtle's shell forming its underside