Volunteers fast to get gift (6)
I believe the answer is:
talent
'gift' is the definition.
(I know that gift can be written as talent)
'volunteers fast' is the wordplay.
'volunteers' becomes 'TA' (abbreviation for Territorial Army).
'fast' becomes 'lent' (Lent is a period of fasting in Christianity).
'ta'+'lent'='TALENT'
'to get' acts as a link.
(Other definitions for talent that I've seen before include "Natural ability or gift" , "Special aptitude for the old Greek money" , "Clever folk" , "Type of scout - innate ability - old Greek money" , "Innate aptitude" .)