Looks up primates and judge in Split (8)
I believe the answer is:
separate
'split' is the definition.
('separate' can be a synonym of 'split')
'looks up primates and judge' is the wordplay.
'looks up' says the letters should be written in reverse (I've seen 'looking up' mean this).
'primates' becomes 'apes' (ape is a kind of primate).
'and' says to put letters next to each other.
'judge' becomes 'rate' (rating is a kind of judging).
'apes' reversed gives 'sepa'.
'sepa'+'rate'='SEPARATE'
'in' acts as a link.
(Other definitions for separate that I've seen before include "Distinct or discrete" , "Dinstinct or discrete" , "Set apart" , "Standing apart" , "Distinct, not joined" .)