Crossword Genius

A sweeper beginning to be someone (5)

Ross

I believe the answer is:

besom

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

'a sweeper' is the definition.
(I've seen this before)

'beginning to be someone' is the wordplay.
I cannot really understand how this works, but
'be' is within the answer.
The remaining letters 'som' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for besom that I've seen before include "I sweep" , "Lazy woman" , "cleaner?" , "Broom made from twigs tied to a handle" , "Sweeping item" .)

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