cognomen

(n) 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
- Henry's nickname was Slim
byname, moniker, nickname, sobriquet, soubriquet,
(n) the name used to identify the members of a family (as distinguished from each member's given name) family name, last name, surname,

byname moniker nickname sobriquet soubriquet family name last name surname