An environmentalist almost gives consent (5)
I believe the answer is:
agree
'consent' is the definition.
(agreeing is a kind of consenting)
'an environmentalist almost' is the wordplay.
'an' becomes 'a'.
'environmentalist' becomes 'green' (I've seen this before).
'almost' means to remove the last letter (most of the word but not all of it).
'green' with its final letter taken off is 'gree'.
'a'+'gree'='AGREE'
'gives' acts as a link.
(Other definitions for agree that I've seen before include "Arrive at a settlement" , "confess?" , "get on" , "Match; tally" , "suit" .)