Pronunciation: (râr'u-fī"), [key]
—v., -fied, -fy•ing.
1. to make rare or rarer; make less dense: to rarefy a gas.
2. to make more refined, spiritual, or exalted.
to become rare or less dense; become thinned: Moisture rarefies when heated.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.