We don't have synonyms for sirname yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are surname and dirname.
(n) :
Archaic spelling of surname. [The portion of a person's name that is generally hereditary or treated as an indicator of a person's family, which may be shared with other members of the family, or otherwise derived from their names in some fashion; distinguished from that person's given name(s).]
(v) :
Archaic spelling of surname. [(transitive) To give a surname to.]
(n) :
Archaic spelling of surname. [The portion of a person's name that is generally hereditary or treated as an indicator of a person's family, which may be shared with other members of the family, or otherwise derived from their names in some fashion; distinguished from that person's given name(s).]
(v) :
Archaic spelling of surname. [(transitive) To give a surname to.]