Environmental meter, say, for fruit (9)
I believe the answer is:
greengage
'for fruit' is the definition.
(type of plum)
'environmental meter say' is the wordplay.
'environmental' becomes 'green'.
'meter' becomes 'gauge' (I've seen this before).
'say' shows a homophone (sound like).
'gauge' sounds like 'gage'.
'green'+'gage'='GREENGAGE'
(Other definitions for greengage that I've seen before include "Variety of plum" , "Plum-like fruit" , "Garden fruit" , "it's fruity" , "Greenish-yellow type of plum" .)