agnomen
noun
ag·no·men ag-ˈnō-mən 
plural agnomina ag-ˈnä-mə-nə or agnomens
or agnomens : an additional cognomen given to a person by the ancient Romans (as in honor of some achievement)
Word History
Etymology
borrowed from Latin agnōmen, alteration of *adnōmen (by analogy with nōscere "to get to know" : agnōscere "to acknowledge, recognize"), from ad- ad- + nōmen name entry 1 — more at agnize
First Known Use
1654, in the meaning defined above