Advice rejected about long division (5)
I believe the answer is:
split
'division' is the definition.
(I know that split is a type of division)
'advice rejected about long' is the wordplay.
'advice' becomes 'tips' (I've seen this in another clue).
'rejected' says the letters should be written backwards.
'about' indicates putting letters inside.
'long' becomes 'l'.
'tips' back-to-front is 'spit'.
'spit' placed around 'l' is 'SPLIT'.
(Other definitions for split that I've seen before include "Divide (into parts)" , "Dalmatian port" , "Break; leave suddenly" , "somewhere on the Adriatic?" , "Cavil" .)