cognomen cognomen /kɒgˈnoʊmən/

noun

1. The name used to identify the members of a family (as distinguished from each member's given name)  ( cognomen , family name , last name , surname )
   the name used to identify the members of a family (as distinguished from each member's given name)
   
2. A familiar name for a person (often a shortened version of a person's given name)  ( byname , cognomen , moniker , nickname , sobriquet , soubriquet , monicker )
   a familiar name for a person (often a shortened version of a person's given name)
    Joe's mother would not use his nickname and always called him Joseph
   Joe's mother would not use his nickname and always called him Joseph
    Henry's nickname was Slim
   Henry's nickname was Slim