Remaining to one side (4)
I believe the answer is:
left
I believe this clue is a double definition.
'remaining' is the first definition.
(synonyms)
'one side' is the second definition.
(left and right)
'to' acts as a link.
(Other definitions for left that I've seen before include "Sailed from" , "Withdrew - Labour" , "Vacated; political wing" , "Communist?" , "choice at a junction?" .)