Mix company drinks before City rises (8)
I believe the answer is:
coalesce
'mix' is the definition.
('coalesce' can be a synonym of 'mix')
'company drinks before city rises' is the wordplay.
'company' becomes 'co' (abbreviation).
'drinks' becomes 'ales' (I've seen this before).
'before' says to put letters next to each other.
'city' becomes 'ec' (the City of London postcode).
'rises' says the letters should be written backwards.
'ec' written backwards gives 'ce'.
'co'+'ales'+'ce'='COALESCE'
(Other definitions for coalesce that I've seen before include "Grow together, amalgamate" , "Fuse or cause to grow together" , "Merge into one" , "Run together" , "Combine and form one whole, as political parties may" .)