1) Armor plate 2) Armor plating 3) Armour plate 4) Plate armor 5) Plate armour 
[SCUBA] Adolf Hitler and Benito Mussolini in Munich, Germany, ca. June LOCATION: Germany-Munich SOURCE: - NA 242-EB-7-38. bw photo; June 1940; (National Archives photo) retrieved from http://history.acusd.edu/gen/WW2Index/picindex5.html ...
• (n.) A piece, or plate which forms the back of anything, or which covers the back; armor for the back.
[n] - plate armor protecting the back
A plate, usually made from metal, which rests against the diver’s back, and to which the primary scuba cylinders are attached. Held to the body by harness straps over the shoulders and around the waist. It is most often used with a back inflation buoyancy compensator.
noun plate armor protecting the back; worn as part of a cuirass
The rear plate of a cuirass worn with a breastplate.