Aim to have a gin cocktail in conclusion (6)
I believe the answer is:
ending
'conclusion' is the definition.
(I know that conclusion can be written as ending)
'aim to have a gin cocktail' is the wordplay.
'aim' becomes 'end' (both can mean a goal or purpose).
'to have' says to put letters next to each other.
'cocktail' indicates anagramming the letters.
'gin' anagrammed gives 'ing'.
'end'+'ing'='ENDING'
'in' acts as a link.
(Other definitions for ending that I've seen before include "Coda" , "Gin den (anag.)" , "Climax" , "Close - conclusion" , "terminal" .)