Not accustomed to anything brand new (6)

I believe the answer is:

unused

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'brand new' is the definition.
(something brand new has not been used)

'not accustomed' is the wordplay.
'not' becomes 'un' (prefix meaning 'not').
'accustomed' becomes 'used' (I've seen this in other clues).
'un'+'used'='UNUSED'

'to anything' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.

Can you help me to learn more?

(Other definitions for unused that I've seen before include "Unaccustomed" , "Left over" , "Remaining: inexperienced" , "hadn't been exploited" , "Still in wrapper?" .)

I've seen this clue in the Evening Standard.

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