Noble disciple losing heart (4)
I believe the answer is:
peer
'noble' is the definition.
(peer is a kind of noble)
'disciple losing heart' is the wordplay.
'disciple' becomes 'peter' (I've seen this before).
'losing heart' says to hollow out the word (remove centre letters).
'peter' with its middle removed is 'PEER'.
(Other definitions for peer that I've seen before include "Aristocrat" , "Struggle to look" , "Member of the House of Lords" , "Noble; equal" , "Equal - match" .)