The most common and most likely answer to this crossword clue is the 8 letter word MILITANT
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The straight part
We know that "revolutionary" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case revolutionary = militant.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 MILITANT mean?
MILITANT noun- A soldier, a combatant.
- An entrenched or aggressive adherent to a particular cause, now especially a member of a particular ideological faction.
- Specifically, someone who supports the Trotskyist political view expressed in the newspaper Militant, or who engages in aggressive left-wing politics.
- Fighting or disposed to fight; belligerent, warlike.
- Aggressively supporting of a political or social cause; adamant, combative.