<p><strong>Verb</strong></p><ul><li>(used with object) to make rare or rarer; make less dense: to rarefy a gas.</li><li>to make more refined, spiritual, or exalted.</li></ul><p><strong>Verb</strong></p><ul><li>(used without object) to become rare or less dense; become thinned: Moisture rarefies when heated.</li></ul>