[1] : The Collaborative International Dictionary of English v.0.48

backpiece \back"piece`\, backplate \back"plate`\, n. back, n.
   or a. + piece, plate. 
   1. a piece, or plate which forms the back of anything, or
      which covers the back.
      1913 webster

   2. specifically: a piece of plate armor protecting the back;
      -- it is worn as part of a cuirass.
      wordnet 1.5 backrack

[2] : WordNet (r) 2.0

backplate
     n : plate armor protecting the back; worn as part of a cuirass

Backplate >> B Words
Backplate, definition of term: Backplate
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