Company accountant supplies plant (4)
I believe the answer is:
coca
'plant' is the definition.
Both the answer and definition are singular nouns.
Maybe they are linked in a way I don't understand?
'company accountant' is the wordplay.
'company' becomes 'co' (abbreviation).
'accountant' becomes 'CA' (abbreviation for chartered accountant).
'co'+'ca'='COCA'
'supplies' acts as a link.
Can you help me to learn more?
(Other definitions for coca that I've seen before include "South American plant from which a narcotic drug is obtained" , "Drug-yielding shrub" , "S. American drug crop" , "Shrub whose leaves are chewed in the Andes as a stimulant" , "Drug-producing plant" .)