English firm concerned with the environment (3)
I believe the answer is:
eco
'concerned with the environment' is the definition.
(as in eco-friendly)
'english firm' is the wordplay.
'english' becomes 'e' (abbreviation).
'firm' becomes 'co' (a firm is a company).
'e'+'co'='ECO'
(Other definitions for eco that I've seen before include "Umberto - - , novelist" , "Umberto -, Italian author (The Name of the Rose)" , "Concerned with the environment" , "Green prefix" , "Umberto --, Italian writer" .)