The most common and most likely answer to this crossword clue is the 6 letter word CASTRO
I've seen this crossword clue in The Guardian
C
A
S
T
R
O
More clues leading to the result CASTRO
- Some withdrawing support sacked old world leader
- Out of sorts, accused up-and-coming left-winger
- Communist star managed to infiltrate company
- Revolutionary pitched with other ranks on the counter
- Revolutionary vehicle keeps empty spacecraft supplied with oxygen
- Crude suppliers finish off old red lead?
- Country’s leader discarded by revolutionary soldiers
- Revolutionary leader gripped by Vedic astrologers
- Communist statesman spread gold around
Buddy explains!

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 = castro.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.