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.]
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plan of the 4th-century ad
St. Peter's Basilica, Rome, Italy
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2022 by HarperCollins Publishers. All rights reserved.
Indo-European & Semitic Roots Appendices
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