Pronunciation: (sem'ē-mī'nur, sem'ī-, sem"ē-, sem"ī-), [key]
1. Geom.one half the minor axis of an ellipse.
2. Astron.one half the minor axis of the ellipse that one celestial body describes around another, as a planet around the sun.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.