Top ten introduced by a spinning record (4)
I believe the answer is:
apex
'top' is the definition.
(I've seen this before)
'ten introduced by a spinning record' is the wordplay.
'ten' becomes 'x' (roman numeral).
'introduced by' means one lot of letters go next to another.
'spinning' says the letters should be written backwards.
'record' becomes 'ep'.
'ep' reversed gives 'pe'.
'a'+'pe'='ape'
'x' after 'ape' is 'APEX'.
(Other definitions for apex that I've seen before include "climax" , "Uppermost point" , "Culmination" , "Summit - pinnacle" , "white collar union" .)