'Backplate' definitions:

Definition of 'backplate'

From: WordNet
noun
Plate armor protecting the back; worn as part of a cuirass

Definition of 'Backplate'

From: GCIDE
  • 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