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