Uncertain. Compare Frainc-Comtou (the franc-comtois language) and Franco-Provençal mottet (“small boy, young man”) [1633, Dauphiné], perhaps to be connected with Frainc-Comtou and Franco-Provençal moutte, mote (“goat without horns”) of the same origin as French motte, as the goats without horns are the youngest.