The most common and most likely answer to this crossword clue is the 8 letter word ACTIVIST
I've seen this crossword clue in The Guardian
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More clues leading to the result ACTIVIST
Buddy explains!
The straight part
We know that "Militant" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case militant = activist.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 ACTIVIST mean?
ACTIVIST noun- One who is politically active in the role of a citizen; especially, one who campaigns for change.
- One who is conspicuously active in carrying out any occupational or professional functions.
- Behaving as an activist.