Protective plate supports gemstone (8)

I believe the answer is:

brassard

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'protective plate' is the definition.
'brassard' can be an answer for 'plate' (brassard is a kind of plate). I am unsure of the 'protective' bit.

'supports gemstone' is the wordplay.
'supports' becomes 'bras' (I've seen this before).
'gemstone' becomes 'sard' (sard is a kind of gemstone).
'bras'+'sard'='BRASSARD'

Can you help me to learn more?

(Other definitions for brassard that I've seen before include "Armour for the upper arm" , "protection for member" .)

I've seen this clue in The Guardian.

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