The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

   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.
         [1913 Webster]

   2. An appellation added to the original name; an agnomen. "My
      surname, Coriolanus." --Shak.
      [1913 Webster]

   Note: This word has been sometimes written sirname, as if it
         signified sire-name, or the name derived from one's
         father.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

         Another shall subscribe with his hand unto the Lord,
         and surname himself by the name of Israel. --Isa. xliv.
                                                  5.
   [1913 Webster]

         And Simon he surnamed Peter.             --Mark iii.
                                                  16.
   [1913 Webster]

WordNet (r) 3.0 (2006):

surname
    n 1: the name used to identify the members of a family (as
         distinguished from each member's given name) [syn:
         surname, family name, cognomen, last name]