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noun6

1. •
   The rounded east (liturgical east) end of a church that contains or is behind the altar.

   • Our private tour of the cathedral even allowed us to walk through the apse, which most tours don't.
2. •
   The interior portion of this section of the church building, excluding the ambulatory and any apse chapels.
3. •
   A semicircular projection from any building that is similar to a church's apse.

   • The college has an apse that once held a small chapel.
4. •
   The bishop's seat or throne in ancient churches.
5. •
   A reliquary: a case in which the relics of saints are kept.
6. •
   (dialect, no longer used) An aspen tree.