Sharp charm on bracelet's rear beginning to rub (9)
I believe the answer is:
trenchant
'sharp' is the definition.
(I've seen this before)
'charm on bracelet's rear beginning to rub' is the wordplay.
'charm' becomes 'enchant' (enchanting is a kind of charming).
'on' is a charade indicator (letters next to each other).
'rear' indicates one should take the final letters (the back of the word).
'beginning to' suggests taking the first letters.
The last letter of 'bracelet' is 't'.
The initial letter of 'rub' is 'r'.
't'+'r'='tr'
'enchant' after 'tr' is 'TRENCHANT'.
(Other definitions for trenchant that I've seen before include "Incisive in style" , "Showing keenness" , "Distinct" , "Sharp" , "Forthright, vigorous" .)