langue d'oïl

[lahng daw-eel, daw-ee, doil] /lɑ̃g dɔˈil, ˈdɔ i, ˈdɔɪl/
noun
1.
the Romance language of medieval northern France: developed into modern French.
Origin
1695-1705; < French: language of oïl (Old French; compare French oui), yes < Latin hōc ille (fēcit) this he (did)
British Dictionary definitions for langue d'oïl

langue d'oïl

/lɑ̃ɡ dɔj/
noun
1.
the group of medieval French dialects spoken in France north of the Loire; the medieval basis of modern French
Word Origin
literally: language of oïl (the northern form for yes), ultimately from Latin hoc ille (fecit) this he (did)