'Lingua franca' used to name one specific language, not the concept of a shared one

Before it became a generic term for any shared trade language, 'lingua franca' named an actual pidgin — a mix of Italian, French, Spanish, Greek, Arabic and Turkish — that sailors and merchants used across Mediterranean ports for centuries. Its name literally meant 'language of the Franks,' the term used for Western Europeans generally, and the pidgin itself survived in shrinking use into the 19th century before the phrase outlived the language it named.

— Jocelyn Dakhlia, Mediterranean Lingua Franca — Lingua Franca in the Levant, 2008