Fantasy husband off to look for pity once (7)
I believe the answer is:
untruth
'fantasy' is the definition.
(something imagined or untrue)
'husband off to look for pity once' is the wordplay.
'husband' becomes 'h' (abbreviation).
'off' is a deletion indicator ('off' can mean to remove).
'to look for' becomes 'hunt' (to hunt for something is to look for it).
'pity once' becomes 'ruth' (archaic term meaning pity).
'hunt' with 'h' removed is 'unt'.
'unt'+'ruth'='UNTRUTH'
(Other definitions for untruth that I've seen before include "Fiction" , "A lie or false statement" , "Falsehood or lie" , "Fib" , "story" .)