1. Architecture A usually semicircular or polygonal, often vaulted recess, especially the termination of the sanctuary end of a church.
2. Astronomy An apsis.
[Variant of APSIS.]
(click for a larger image)apse
plan of the 4th-century ad
St. Peter's Basilica, Rome, Italy
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.