As written, it is off topic.
Asking the origin of these terms as they relate to D&D is unavoidably a question of designer's intent.
We can list all of the objective historical information about breast plates, but the moment we say, "And this is where Gygax/Crawford/Mearls/Perkins got their inspiration from", we are making an assertion that these people intended to represent those particular historical facts in the world of D&D. Asking if the game's designers were influenced by some historical truth is a question of designer's intent, which is off topic.
The history of breast plates in general is also off topic.
If we divorce the terminology from the game, and just ask, "what is the history of breast plates?", we are no longer asking an RPG question, we're asking a history question, which is better asked at history.se.
What is on topic?
The question as answered by Quadratic Wizard is on topic. Quadratic Wizard answers the question, "What is the development of these terms through the various editions of D&D?" This is on topic. But it is not what the question is asking. The question as written asks only about 5th Edition, and asks how the designers have related the 5th edition material to historical material - a question of designer intent.
The question needs to be reworded so as to ask about the development of the terminology through editions, otherwise it is off topic.