lin ‧ gua fran ‧ ca /ˌlɪŋɡwə ˈfræŋkə/ BrE AmE noun [countable, usually singular]
[ Date: 1600-1700 ; Language: Italian ; Origin: 'tongue of the Franks' ]
a language used between people whose main languages are different:
English is the lingua franca in many countries.