Shortage giving a bully heart for a time (6)
I believe the answer is:
ullage
'shortage' is the definition.
(thesaurus)
'a bully heart for a time' is the wordplay.
'heart' indicates the central letters.
'for' is a charade indicator (letters next to each other).
'a time' becomes 'age' (an age is a period of time).
The centre of 'bully' is 'ull'.
'ull'+'age'='ULLAGE'
'giving' acts as a link.
(Other definitions for ullage that I've seen before include "The amount by which a bottle falls short of being full" , "Loss by evaporation or leakage" , "dregs" , "Amount by which a liquid container falls short of being full" , "shortfall" .)