Volunteers fast gift (6)
I believe the answer is:
talent
'gift' is the definition.
('talent' can be a synonym of 'gift')
'volunteers fast' is the wordplay.
'volunteers' becomes 'ta' (abbreviation for Territorial Army).
'fast' becomes 'lent' (I've seen this before).
'ta'+'lent'='TALENT'
(Other definitions for talent that I've seen before include "Natural endowment" , "money no longer usable" , "Natural ability or gift" , "Coin at one time" , "Flair, aptitude" .)