Overplus, n.
Etymology: [Over + L. plus more. See Plus, and cf. Surplus.]
That which remains after a supply, or beyond a quantity proposed; surplus. Shak. "The overplus of a great fortune." Addison.
Shades of meaning
Fernald has no entry of its own for overplus; he lists it under excess.
Where he writes about it:
Overplus and superabundance denote in the main a satisfactory, and superfluity an undesirable, excess; lavishness and profusion, a generous, bountiful, or amiable excess; as, a profusion of fair hair; lavishness of hospitality. — from excess