A Dictionary of Greek and Roman Antiquities/Absis
ABSIS or APSIS (the former more correct in Latin) (ἁψίς), in its literal meaning from ἅπτω, is a fastening of any kind; for example, the meshes of a net. (Hom. il. 5.487.) It was applied specially to the joining together the extremities of a piece of wood, so as to give it the shape of a bow; and hence it came to signify anything of that shape, such as a bow, an arch, or a wheel. (Hes. Op. 424; Hdt. 4.72.) A potter's wheel is described, in the Anthology, as κύκλος ἁψῖδος. The next transition of meaning is to anything vaulted (for example, ἡ ὑπουρανία ἁψίς, the vault of heaven, Plat. Phaedr. p. 247 b); and in this sense it was adopted in architecture, first, for any building or portion of a building of a circular form, or vaulted (Plin. Ep. 2.17.18), and more especially for the circular and vaulted end of a Basilica. (Paul. Nol. Ep. 12; Augustin, Ep. 203; Isid. Orig. 15.8.) For the application of the word in Christian churches, see Dict. of Christ. Ant. S. V. APSE. [P.S]