A liberal drink before sum (5)
I believe the answer is:
total
'sum' is the definition.
(I know that sum can be written as total)
'a liberal drink before' is the wordplay.
'liberal' becomes 'l' (abbreviation).
'drink' becomes 'tot' (a small alcoholic drink).
'before' says to put letters next to each other.
'a'+'l'='al'
'al' after 'tot' is 'TOTAL'.
(Other definitions for total that I've seen before include "Completely destroy" , "Not qualified" , "Utter" , "Absolute; sum" , "Aggregate amount" .)