Main Entry: rar·e·fy

Variant(s): also rar·i·fy \ˈrar-ə-ˌfī, ˈrer-\

Function: verb

Inflected Form(s): rar·e·fied also rar·i·fied; rar·e·fy·ing also rar·i·fy·ing

transitive verb

: to make rare, thin, porous, or less dense : to expand without the addition of matter

intransitive verb

: to become less dense