Crossword Genius

With no humility, half of mum's brothers advanced (11)

Ross

I believe the answer is:

unchastened

I'm a little stuck... Click here to teach me more about this clue!

'with no humility' is the definition.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

I've seen this clue in The Everyman puzzle in The Observer.
Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.