Surplus is a related term of residue.
In legal|lang=en terms the difference between surplus and residue
is that
surplus is (legal) assets left after liabilities and debts, including capital stock have been deducted while
residue is (legal) whatever property or effects are left in an estate after payment of all debts, other charges and deduction of what is specifically bequeathed by the testator.
As nouns the difference between surplus and residue
is that
surplus is that which remains when use or need is satisfied, or when a limit is reached; excess; overplus while
residue is whatever remains after something else has been removed.
As an adjective surplus
is being or constituting a surplus; more than sufficient; as, surplus revenues; surplus population; surplus words.