Monkey stopping to beat one set of drums (7)
I believe the answer is:
timpani
'set of drums' is the definition.
'monkey stopping to beat one' is the wordplay.
'monkey' becomes 'imp' (synonyms).
'stopping' means one lot of letters goes inside another (stopping can mean blocking a gap).
'to beat' becomes 'tan' (I've seen this before).
'one' becomes 'i' (roman numeral).
'imp' put into 'tan' is 'timpan'.
'timpan'+'i'='TIMPANI'
(Other definitions for timpani that I've seen before include "set of instruments" , "part of kitchen?" , "Mini tap on a large drum" , "Main pit (anag) - drums" , "Those beaten" .)