IPA: /ˈbrɛstˌpleɪt/
KK: /ˈbrɛstˌpleɪt/
A protective piece of armor that covers the front of the body, often made of metal, and used in battle or as part of ceremonial dress.
The knight wore a shiny breastplate to protect himself in battle.
Breastplate → It is formed from "breast" (from Old English "brēost", meaning the front part of the body) and "plate" (from Old French "plate", meaning a flat piece of metal or armor). The word "breastplate" refers to a protective armor piece that covers the front of the body.
Think of the 'front part of the body' ('breast') being covered by a 'flat piece of armor' ('plate') — that's what a breastplate does.