Old boy: one imparting charm (3)

I believe the answer is:

obi

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'imparting charm' is the definition.
'obi' can be an answer for 'charm' (also obeah, type of sorcery). I am not certain of the 'imparting' bit.

'old boy one' is the wordplay.
'old boy' becomes 'OB' (abbreviation for a private school 'old boy').
'one' becomes 'i' (Roman numeral).
'ob'+'i'='OBI'

Can you help me to learn more?

(Other definitions for obi that I've seen before include "Kimono accessory" , "exotic waistband" , "belt" , "Broad Japanese sash" , "Material band" .)

I've seen this clue in The Times.

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