What does the word apse mean?

Usage examples for apse

  1. The eastern apse, too, has been replaced by a square end. – England of My Heart--Spring by Edward Hutton
  2. One distinctly northern feature there is; namely, the singular effect given by the double apse of the nave and choir, reminiscent mainly of the Rhine builders, that of the eastern end being much the older. – The Cathedrals of Northern France by Francis Miltoun