ap·si·dal /ˈæpsədḷ/
  (a.)apse的
  Ap·si·dal a.
  1. Astron. Of or pertaining to the apsides of an orbit.
  2. Arch. Of or pertaining to the apse of a church; as, the apsidal termination of the chancel.
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  apsidal
       adj : of or relating an apse