One hundred remaining to be split (5)
I believe the answer is:
cleft
'be split' is the definition.
(cleft can mean split or cloven)
'one hundred remaining' is the wordplay.
'one hundred' becomes 'c' (Roman numeral).
'remaining' becomes 'left' (synonyms).
'c'+'left'='CLEFT'
'to' is the link.
(Other definitions for cleft that I've seen before include "Split or indentation" , "Chin split" , "Narrow gap" , "Opening, fissure" , "Narrow opening" .)