Source : Webster's Revised Unabridged Dictionary (1913)

Surname \Sur"name`\, n. [Pref. sur + name; really a substitution
   for OE. sournoun, from F. surnom. See {Sur-}, and {Noun},
   {Name}.]
   1. A name or appellation which is added to, or over and
      above, the baptismal or Christian name, and becomes a
      family name.

   Note: Surnames originally designated occupation, estate,
         place of residence, or some particular thing or event
         that related to the person; thus, Edmund Ironsides;
         Robert Smith, or the smith; William Turner. Surnames
         are often also patronymics; as, John Johnson.

   2. An appellation added to the original name; an agnomen.
      ``My surname, Coriolanus.'' --Shak.

   Note: This word has been sometimes written sirname, as if it
         signified sire-name, or the name derived from one's
         father.

Surname \Sur*name"\, v. t. [imp. & p. p. {Surnamed}; p. pr. &
   vb. n. {Surnaming}.] [Cf. F. surnommer.]
   To name or call by an appellation added to the original name;
   to give a surname to.

         Another shall subscribe with his hand unto the Lord,
         and surname himself by the name of Israel. --Isa. xliv.
                                                  5.

         And Simon he surnamed Peter.             --Mark iii.
                                                  16.

Source : WordNet®

surname
     n : the name used to identify the members of a family (as
         distinguished from each member's given name) [syn: {family
         name}, {cognomen}, {last name}]