Greek character leading insignificant rebellion (6)
I believe the answer is:
Here is my best explanation:
'rebellion' is the definition.
(mutiny is a kind of rebellion)
'greek character leading insignificant' is the subsidiary indication.
'greek character' becomes 'mu' (**).
'leading' says to put letters next to each other.
'insignificant' becomes 'tiny' (I've seen this before).
(Other definitions for mutiny that I've seen before include "Rebellion by sailors or soldiers", "Rebellion as on Bligh's Bounty", "Open rebellion against constituted authority", "revolt", "Insurrection", "Rebellion in the armed forces", "Military rebellion", "Open rebellion by sailors or soldiers", "Rising, rebellion" and "Armed forces rebellion".)