Father has an allowance -- that's sweet (8)
I believe the answer is:
fragrant
'sweet' is the definition.
('fragrant' can be similar in meaning to 'sweet')
'father has an allowance' is the wordplay.
'father' becomes 'fra'.
'has' is a charade indicator (letters next to each other).
'an allowance' becomes 'grant' (I've seen this before).
'fra'+'grant'='FRAGRANT'
'that's' is the link.
(Other definitions for fragrant that I've seen before include "Pleasant-smelling" , "Pleasantly smelly?" , "bouquet" , "Perfumed" , "Having pleasant odour" .)