breastplate

n. armor for the front of the torso

This can also refer to a piece of riding equipment, see Breastplate (tack).Breastplates are devices worn over the torso either as protective armor or as an item of religious significance. A breastplate is sometimes worn by mythological beings as a distinctive item of clothing.
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Noun
1. armor plate that protects the chest; the front part of a cuirass
(synonym) aegis, egis
(hypernym) armor plate, armour plate, armor plating, plate armor, plate armour
(hyponym) plastron
(part-holonym) body armor, body armour, suit of armor, suit of armour, coat of mail, cataphract

(n.)
A strap that runs across a horse's breast.
  

(n.)
A plate of metal covering the breast as defensive armor.
  

(n.)
A piece against which the workman presses his breast in operating a breast drill, or other similar tool.
  

(n.)
A part of the vestment of the high priest, worn upon the front of the ephod. It was a double piece of richly embroidered stuff, a span square, set with twelve precious stones, on which were engraved the names of the twelve tribes of Israel. See Ephod.
  

Originally evolving out of the cote of plates as the size on each individual plate increased and the front plate was increasingly globular, the breastplate was fully formed by 1360 or so but was not in wide use until the 1380s. This globular design provided an effective glancing surface that deflected both hand and missile weapons. During the 1360-1400 period it was seen both in the covered and open form, often worn over a gambeson , though it was sometimes worn under as well. There are illustrations that show the breastplate worn both over and under of an outer houpelande , but by 1400 the usual practice was to attach the breastplate to the backplate and provide faulds for the defense of the hip, the solution widely implemented during the whole of the 15th century. In the middle of the 14th century a "stop rib" was often added to the area just below the neck to keep lances and sword points from skipping up into the throat. During the same period, a lance rest was added to enable the knight to more easily couch the lance for a longer period of time. The edge around the neck and arm openings was rolled outward, sometimes over a wire, to guard against chafing and to help deflect a weapon from these vulnerable areas.
15th century breastplates increased the size of the rolls around the neck and arm hole, and experiments were made with making the breastplate from multiple pieces to increase the knight's mobility while simultaneously increasing the protection.