In the sack, husband hot for booty (6)
I believe the answer is:
behind
'booty' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'in the sack husband hot' is the wordplay.
'in' is an insertion indicator.
'the sack' becomes 'bed' ('in the sack' means 'in bed').
'husband' becomes 'h'.
'hot' becomes 'in' (both can mean fashionable).
'h'+'in'='hin'
'bed' enclosing 'hin' is 'BEHIND'.
'for' is the link.
Can you help me to learn more?
(Other definitions for behind that I've seen before include "bum" , "Hidden by; bottom" , "Running late" , "Not in front" , "Rear - losing" .)