Sentimentality? Head off for boozer! (4)
I believe the answer is:
lush
'boozer' is the definition.
(synonyms)
'sentimentality? head off' is the wordplay.
'sentimentality?' becomes 'slush' (I've seen this before).
'head off' means to remove the first letter.
'slush' with its initial letter taken off is 'LUSH'.
'for' is the link.
(Other definitions for lush that I've seen before include "one wants a lot to drink" , "Of grass, growing thick and strong" , "Luxuriant (vegetation)" , "Drunk" , "Succulent - soak" .)