Split remaining under canine’s crown (5)
I believe the answer is:
cleft
'split' is the definition.
(synonyms)
'remaining under canine's crown' is the wordplay.
'remaining' becomes 'left' (synonyms).
'under' says to put letters next to each other.
'crown' suggests taking the first letters (crown can mean the top of something).
The first letter of 'canine' is 'c'.
'left' put after 'c' is 'CLEFT'.
(Other definitions for cleft that I've seen before include "Split; fissure" , "Split or indentation" , "division" , "Chin split" , "Split, divided" .)