Main Entry:

rar·e·fy

Variant(s):

also rar·i·fy \ˈrer-ə-ˌfī\

Function:

verb

Inflected Form(s):

rar·e·fied; rar·e·fy·ing

Etymology:

Middle English rarefien, rarifien, modification of Latin rarefacere, from rarus rare + facere to make — more at do

Date:

14th century

transitive verb 1 : to make rare, thin, porous, or less dense : to expand without the addition of matter 2 : to make more spiritual, refined, or abstruse intransitive verb : to become less dense