Plant with yellow spike (5)
I believe the answer is:
'plant' is the definition.
(orpin is a kind of plant)
'with yellow spike' is the wordplay.
'with' is a charade indicator (letters next to each other).
'yellow' becomes 'or' (heraldic term).
'spike' becomes 'pin' (pinning is a kind of spiking).
'or' put next to 'pin' is 'ORPIN'.
(Other definitions for orpin that I've seen before include "Purple, broad-leafed stonecrop" , "Plant" , "Variety of stonecrop" , "Bloomer" , "Stonecrop that's purple" .)