langue d'oïl
/lɒ̃(ɡ) ˈdɔɪl
/ /lɑ̃ɡ dɔjl/noun [mass noun]
The form of medieval French spoken north of the Loire, generally characterized by the use of oïl to mean ‘yes’, and forming the basis of modern French.
Origin
From Old French langue 'language' (from Latin lingua 'tongue'), d' (from de 'of'), and oïl (from Latin hoc ille) 'yes'. Compare with langue d'oc.