de;cade pronunciation: function: noun etymology: middle english, from middle french décade, from late latin decad-, decas, from greek dekad-, dekas, from dekadate: 15th century 1 : a group or set of 10: as a : a period of 10 years b : a division of the rosary that consists primarily of 10 hail marys 2 : a ratio of 10 to 1 : order of magnitude— de;cad;al adjective