langue d'oc
Concise Oxford English Dictionary © 2008 Oxford University Press:
langue d'oc /lɒ̃(g) ˈdɒk/
▶noun the form of medieval French spoken south of the Loire, generally characterized by the use of oc to mean ‘yes’, and forming the basis of modern Provençal.
– origin OFr. lit. ‘language of oc’ (see above).
'langue d'oc' also found in these Oxford entries:

