cognomen

noun

1. the name used to identify the members of a family (as distinguished from each member's given name)

   Synonym:    surnamefamily namelast name

2. a familiar name for a person (often a shortened version of a person's given name)
   1. Joe's mother would not use his nickname and always called him Joseph
   2. Henry's nickname was Slim

   Synonym:    nicknamemonikersobriquetsoubriquetbyname