Late Middle English. From Middle French (Normandy) chymois, chemois chief country house or dwelling, mansion house, reduced variants of Middle French (Picardy and Normandy) chief mes, chief mais, etc. from post-classical Latin caput mansus, caput mansi from classical Latin caput head + post-classical Latin mansus, mansi, genitive of mansus (declined as 4th or 2nd declension respectively).