Member of whole group (3)
I believe the answer is:
'member' is the definition.
(member can mean a limb)
'of whole group' is the wordplay.
'of' indicates a hidden word.
'LEG' is hidden within 'whole group'.
(Other definitions for leg that I've seen before include "prop" , "Run < on" , "Lower limb" , "Support; cricket side" , "Stage (of race)" .)