Drum mostly banned by Rossini at first (5)
I believe the answer is:
tabor
'drum' is the definition.
(tabor is a kind of drum)
'mostly banned by rossini at first' is the wordplay.
'mostly' means to remove the last letter.
'banned' becomes 'taboo' (I've seen this before).
'by' is a charade indicator (letters next to each other).
'at first' suggests taking the first letters.
The initial letter of 'rossini' is 'r'.
'taboo' with its final letter taken off is 'tabo'.
'tabo'+'r'='TABOR'
(Other definitions for tabor that I've seen before include "beaten with stick" , "Mount" , "Type of drum" .)