Two firms meet over a drink (5)
I believe the answer is:
cocoa
'drink' is the definition.
(I know that cocoa is a drink)
'two firms meet over a' is the wordplay.
'two firms' can mean two replacements for 'firm'.
'firm' becomes 'co' (a firm is a company).
'firm' becomes 'co' (a firm is a company).
'meet' is a charade indicator (letters next to each other).
'over' says to put letters next to each other (in a down clue, some letters go over others).
'co'+'co'+'a'='COCOA'
(Other definitions for cocoa that I've seen before include "Chocolate-like drink" , "Hot beverage" , "Lightish brown colour of a drink" , "Chocolate powder" , "Bean used in making chocolate" .)