cognomen
Concise Oxford English Dictionary © 2008 Oxford University Press:
cognomen /kɒgˈnəʊmən/
▶noun an extra personal name given to an ancient Roman citizen, functioning rather like a nickname and often passed from father to son.
– origin L., from co- ‘together with’ + gnomen, nomen ‘name’.
'cognomen' also found in these Oxford entries:
