lingua franca
\LING-gwuh FRANG-kuh\,
noun:
1. any language that is widely used as a means of communication among speakers of other languages.
2. (initial capital letter) the Italian-Provençal jargon (with elements of Spanish, French, Greek, Arabic, and Turkish) formerly widely used in eastern Mediterranean ports.
...though Ukrainian may be the official language, Russian is the lingua franca. Crimea may be politically part of Ukraine, but it identifies with Russia emotionally and psychologically.
-- Cathy Newman, "After Ukraine Crisis, Why Crimea Matters," National Geographic, 2014
As the guys drank up, with only Jason abstaining, the conversation skipped from fishing to lacrosse to friends in common, the easy lingua franca of young men from the prep-school dominion.
-- Tad Friend, "Thicker Than Water," The New Yorker, 2014
This term comes from the Italian literally meaning "Frankish tongue." It's existed in English since the 1600s.
Dictionary.com
