A gold-plated propeller blade (3)
I believe the answer is:
oar
'propeller blade' is the definition.
'oar' can be an answer for 'blade' (blade is the word for oar in competitive rowing). I'm not sure about the 'propeller' bit.
'a gold-plated' is the wordplay.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'plated' is an insertion indicator (plated can mean covered or coated).
'a' placed inside 'or' is 'OAR'.
Can you help me to learn more?
(Other definitions for oar that I've seen before include "Rowing device" , "Bladed pole" , "Pusher" , "propels floating craft" , "Pole for rowing" .)