v.
Variant: also rar · i · fy
Pronunciation: ' rer- ə - ˌ f ī
Function: verb
Inflected Form: -fied ; -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