RAR'EFY, verb transitive [Latin rarefacio; rarus, rare, and facio, to make.] To make thin and porous or less dense; to expand or enlarge a body without adding to it any new portion of its own matter; opposed to condense. RAR'EFY, verb intransitive To become thin and porous.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI