rarefy
verb
rar·e·fy ˈrer-ə-ˌfī 
variants or less commonly rarify
rarefied; rarefying
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
Example Sentences
Recent Examples on the Web As rarefied as his work was, as an individual and as a spirit there was something to celebrate — and yet there were foibles and missteps along the way too, so there was real good drama there. 
Tim Greiving, latimes.com, 3 June 2019 But in 2003, when Clear was founded, biometric technology was rarefied, known to the public mostly through science fiction films. Claire Martin, New York Times, 8 Sep. 2017 Touching on issues of artistic survival and the porous boundary between work and pleasure, Ms. Subrin, an accomplished visual artist and filmmaker, sifts addiction, celebrity and the plight of the aging actress into something rarefied yet real. Jeannette Catsoulis, New York Times, 21 Mar. 2017 And so while his techniques and ingredients are rarefied, Mr. Lenn’s food is decidedly less luxe in Knoxville, designed to appeal to a broader audience. Jane Black, New York Times, 20 June 2017 But Mr. Affleck loves the Carlyle’s rarefied throwback allure. Cara Buckley, New York Times, 4 Nov. 2016 And now, thanks to our constantly rarefying visual culture, the young actormen have become precious too — choosing carefully fitted suits or statement bespokery, not a stray hair on their head or face. Mike Albo, Esquire, 4 Apr. 2012 See More
Tim Greiving, latimes.com, 3 June 2019 But in 2003, when Clear was founded, biometric technology was rarefied, known to the public mostly through science fiction films. Claire Martin, New York Times, 8 Sep. 2017 Touching on issues of artistic survival and the porous boundary between work and pleasure, Ms. Subrin, an accomplished visual artist and filmmaker, sifts addiction, celebrity and the plight of the aging actress into something rarefied yet real. Jeannette Catsoulis, New York Times, 21 Mar. 2017 And so while his techniques and ingredients are rarefied, Mr. Lenn’s food is decidedly less luxe in Knoxville, designed to appeal to a broader audience. Jane Black, New York Times, 20 June 2017 But Mr. Affleck loves the Carlyle’s rarefied throwback allure. Cara Buckley, New York Times, 4 Nov. 2016 And now, thanks to our constantly rarefying visual culture, the young actormen have become precious too — choosing carefully fitted suits or statement bespokery, not a stray hair on their head or face. Mike Albo, Esquire, 4 Apr. 2012 See More Word History
Etymology
Middle English rarefien, rarifien, modification of Latin rarefacere, from rarus rare + facere to make — more at do
First Known Use
14th century, in the meaning defined at transitive sense 1
Medical Definition
rarefy
verb
rar·e·fy
variants also rarify
ˈrar-ə-ˌfī, ˈrer-
rarefied also rarified; rarefying also rarifying
transitive verb
: to make rare, thin, porous, or less dense : to expand without the addition of matter
intransitive verb
: to become less dense