transept

n. [ Pref. trans- + L. septum an inclosure. See Septum. ] (Arch.) The transversal part of a church, which crosses at right angles to the greatest length, and between the nave and choir. In the basilicas, this had often no projection at its two ends. In Gothic churches these project greatly, and should be called the arms of the transept. It is common, however, to speak of the arms themselves as the transepts. [ 1913 Webster ]