Right knife radical, the side-form of
刀 placed at the right edge. Picturing a blade, it supplies the action of cutting away - what is left after the blade has done its work is the remainder. Hence
剩 'to be left over, surplus, remaining', as in
剩下 (be left),
剩饭 (leftover food). Joins
删,
割,
副 in the cut-and-trim family.
