n. A payment in excess of what is just or required.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. a payment larger than needed or expected
n. the act of paying too much
Word Usage
"Frankly, I'm wondering where this vaunted overpayment is going, because as far as I can tell, it disappears every month between DFAS (The Defense Finance and Accounting Service) and my bank account."