Foremost of strategically key eco warriors shows bias (4)
I believe the answer is:
skew
'bias' is the definition.
(synonyms)
'foremost of strategically key eco warriors' is the wordplay.
'foremost of' says to take the initial letters.
The initial letters of 'strategically key eco warriors' is 'SKEW'.
'shows' is the link.
(Other definitions for skew that I've seen before include "Place obliquely" , "Make biased or distorted" , "Place(d) obliquely" , "Turn or twist around" , "Slant, bias" .)