Not obligate; optional, discretionary or elective.
That grants permission or power to do something.
Able to perform a particular life function, or to live generally, in more than one way.
Of or relating to faculty, especially to mental faculty.
At which a given function is positive.
Remaining; left behind; extra; in reserve.
Something left behind; an excess or remainder.
Remaining after a meal is complete or eaten for a later meal or snack.