Chest and back armour (7)
I believe the answer is:
cuirass
'chest and back armour' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for cuirass that I've seen before include "Large piece of armour enveloping the upper body" , "Upper-body armour piece" , "Some mail" , "Item of armour" , "Chest and back armour" .)