Definition of: rarefy

(râr′ə·fī) v. ·fied, ·fy·ing v.t.
1. To make rare, thin, less solid, or less dense; expand by dispersion of the particles.
2. To refine or purify.
—v.i.
3. To become rare, thin, or less solid.
4. To become more pure. [<F raréfier <L rarefacere <rarus rare + facere make]
—rar′e·fi′a·ble adjective