Takes off (6)
(Other definitions for splits that I've seen before include "Shares" , "Separates or cuts with a sharp tool" , "Cleaves or divides" , "Breaks into two parts as with axe" , "Acrobatic feat -- schisms" .)
'takes off' is the definition.
('subtract' can be a synonym of 'take off')
This is all the clue.
(Another definition for subtracts that I've seen is " Deducts, takes away".)