Wordnet 3.0
NOUN (1)
1. 
 an Italian title of respect for a man; 
 equivalent to the English `sir'; 
 used separately (not prefixed to his name); 
The Collaborative International Dictionary of English v.0.48:
Signor \Si*gnor"\, Signore \Si*gno"re\, n. [It. See Seignior.]
   Sir; Mr.; -- a title of address or respect among the
   Italians. Before a noun the form is Signor.
   [1913 Webster]
WordNet (r) 3.0 (2006):
signore
    n 1: an Italian title of respect for a man; equivalent to the
         English `sir'; used separately (not prefixed to his name)