[1] : The Collaborative International Dictionary of English v.0.48

apse \apse\ a^ps, n.; pl. apses a^p"se^z. see
   apsis.
   1. arch.
      a a projecting part of a building, esp. of a church,
          having in the plan a polygonal or semicircular
          termination, and, most often, projecting from the east
          end. in early churches the eastern apse was occupied
          by seats for the bishop and clergy. hence:
      b the bishop's seat or throne, in ancient churches.
          1913 webster

   2. a reliquary, or case in which the relics of saints were
      kept.
      1913 webster

   note: this word is also written apsis and absis.
         1913 webster
see also:
apsis apsis absis 

[2] : The Collaborative International Dictionary of English v.0.48

apsis \ap"sis\ a^p"si^s, n.; pl. apsides
   a^p"si^d=ez. see apse. l. apsis, absis, gr.
   "apsi`s, "apsi^dos, a tying, fastening, the hoop of a wheel,
   the wheel, a bow, arch, vault, fr. "a`ptein to fasten.
   1. astron. one of the two points of an orbit, as of a
      planet or satellite, which are at the greatest and least
      distance from the central body, corresponding to the
      aphelion and perihelion of a planet, or to the apogee and
      perigee of the moon. the more distant is called the higher
      apsis; the other, the lower apsis; and the line joining
      them, the line of apsides.
      1913 webster

   2. math. in a curve referred to polar co"ordinates, any
      point for which the radius vector is a maximum or minimum.
      1913 webster

   3. arch. same as apse.
      1913 webster
see also:
apsides apse 

[3] : WordNet (r) 2.0

apsis
     n : a domed or vaulted recess or projection on a building
         especially the east end of a church; usually contains the
         altar syn: apse
     also: apsides pl
see also:
apse apsides 

Apsis >> A Words
Apsis, definition of term: Apsis
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