Apse

aps, n. an arched semicircular or polygonal rece at the east end of the choir of a church—here, in the Roman basilica, stood the prætor's chair.— adj. Ap′sidal .— n. Apsid′iole , a secondary apse, as one of the apses on either side of the central or main apse in a church of triapsidal plan. [See Apsis .]