Queen's in study endlessly drinking alcohol (6)
I believe the answer is:
regina
'queen's' is the definition.
(I've seen this before)
'study endlessly drinking alcohol' is the wordplay.
'study' becomes 'read' (synonyms).
'endlessly' means to remove the last letter.
'drinking' is an insertion indicator.
'alcohol' becomes 'gin' (gin is a kind of alcohol).
'read' with its final letter taken off is 'rea'.
'rea' enclosing 'gin' is 'REGINA'.
'in' acts as a link.
(Other definitions for regina that I've seen before include "our head of state" , "Queen in legal issues" , "Reigning queen's title" , "in Canada" , "Queen (in law cases)" .)