Pronunciation: (ap'sis), [key]
—pl. -si•desPronunciation: (-si-dēz"). [key]
1. Astron.either of two points in an eccentric orbit, one (higher apsis) farthest from the center of attraction, the other (lower apsis) nearest to the center of attraction.
2. Archit.an apse.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.