What is the Latin word for rarefy?

The usual Latin words for “rarefy” are rārēfaciō, extenuō. The right choice depends on the sense; see the distinctions below.

English → Latin

“rarefy” in Latin

rārēfaciōto rarefy extenuōto thin, reduce, diminish

The English word rarefy itself goes back to Latin rārus, through rarefacere.

Riddle & Arnold A Copious and Critical English–Latin Lexicon, 1864

rarefy

rarefacere: to be rarefied, rarescere (of clouds, moisture, etc.): extenuari: rarefied air, aer extenuatus.

Quick answer

What is the Latin word for rarefy?: The usual Latin words for “rarefy” are rārēfaciō, extenuō. The right choice depends on the sense; see the distinctions below.

Entry from J. E. Riddle & T. K. Arnold, A Copious and Critical English–Latin Lexicon (rev. C. Anthon, New York: Harper, 1864), digitised by Fergus J. P. Walsh, CC BY-SA 4.0; Latin markup adapted by latindictionary.co.