to make rare or rarer; make less dense: to rarefy a gas.
to make more refined, spiritual, or exalted.
verb (used without object)
to become rare or less dense; become thinned: Moisture rarefies when heated.
Origin: 1350–1400;Middle Englishrarefien < Middle Frenchrarefier < Latinrārēfacere, equivalent to rārē-, combining form of rārusrare1 (for expected rāri-; orig. of -ē- unclear) + facere to make; see -fy