cognomen Meaning, Definition & Usage

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

WordNet

Cog*no"men noun
Etymology
L.: co- + (g)nomen name.
Definitions
  1. The last of the three names of a person among the ancient Romans, denoting his house or family.
  2. (Eng. Law) A surname.

Webster 1913