Pronunciation: (kē'stōn"), [key]
1. the wedge-shaped piece at the summit of an arch, regarded as holding the other pieces in place.
2. something on which associated things depend: the keystone of one's philosophy.
3. Also called key'stone sack". Baseball Slang.See second base (def. 1).
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.