Volunteer GI deputy returns to hold line (8)
I believe the answer is:
pedigree
'line' is the definition.
(I know that line can be written as pedigree)
'volunteer gi deputy returns to hold' is the wordplay.
'to hold' indicates the answer is hidden within the clue (I've seen 'holding' mean this).
'returns' shows that the letters should be reversed in order.
'eergidep' is hidden within 'volunteer gi deputy'.
'eergidep' back-to-front is 'PEDIGREE'.
(Other definitions for pedigree that I've seen before include "Breeding; descent" , "Ancestry - genealogy" , "Record of descent" , "Line of decent or ancestry" , "bloodline" .)