Wood plate a knight holds (4)
I believe the answer is:
teak
'wood' is the definition.
(type of timber)
'plate a knight holds' is the wordplay.
'holds' indicates the answer is hidden within the clue.
'TEAK' can be found hidden inside 'plate a knight'.
(Other definitions for teak that I've seen before include "Strong heavy wood of an Asian tree" , "Type of wood" , "Quality timber" , "Hard durable wood" , "Hard wood used for furniture" .)