du·o·den·a·ry \|d(y)üə|denərē, -dēn-\adjective Etymology: Latin duodenarius, from duodeni twelve each (from duodecim twelve) + -arius -ary — more at duodecennial 1.: containing 12 < a duodenary cycle of years > 2.: based on the number 12 < a duodenary system of computation >