Tight low-necked garment not having Queen's acceptance (15)
I believe the answer is:
acknowledgement
'acceptance' is the definition.
(acknowledgement is a kind of acceptance)
'tight low-necked garment not having queen's' is the wordplay.
'tight' is an anagram indicator (tight can mean drunk).
'not having' is a deletion indicator.
'queen' becomes 'r' (r is abbreviation regina. e.g. in ER ).
'low'+'necked'+'garment'='lowneckedgarment'
'lowneckedgarment' with 'r' taken out is 'lowneckedgament'.
'lowneckedgament' with letters rearranged gives 'ACKNOWLEDGEMENT'.
(Other definitions for acknowledgement that I've seen before include "admission" , "Confession; thanks" , "profession" .)