The most common and most likely answer to this crossword clue is the 3 plus 7 letter word ECO WARRIOR
I've seen this crossword clue in The Daily Telegraph
E
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The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ECO WARRIOR mean?
ECO WARRIOR noun- An environmentalist who places a greater emphasis upon taking practical action, rather than upon theoretical considerations, in order to advance an ecological ideology.