Source : Webster's Revised Unabridged Dictionary (1913)

Lingua Franca \Lin"gua Fran"ca\ (l[i^][ng]"gw[.a]
   fr[a^][ng]"k[.a]). [It., prop., language of the Franks.]
   The commercial language of the Levant, -- a mixture of the
   languages of the people of the region and of foreign traders.

Lingua Franca \Lin"gua Fran"ca\
   Any hybrid or other language used over a wide area as a
   common or commercial tongue among peoples of different
   speech.

Source : WordNet®

lingua franca
     n : a common language used by speakers of different languages;
         "Koine is a dialect of ancient Greek that was the lingua
         franca of the empire of Alexander the Great and was
         widely spoken throughout the eastern Mediterranean area
         in Roman times" [syn: {interlanguage}, {koine}]