late 14c., rarefien, "make thin, reduce the density of," from Old French rarefier (14c.) and directly from Medieval Latin rarificare, from Latin rarefacere "make thin, make rare," from rarus "rare, thin" (see rare (adj.1)) + facere "to make" (from PIE root *dhe- "to set, put"). Intransitive sense of "become less dense" is from 1650s. Related: Rarefied; rarefiable.
Entries linking to rarefy
[thin, few, unusual] late 14c., "thin, airy, porous" (opposed to dense); mid-15c., "few in number and widely separated, sparsely distributed, seldom found, very infrequent;" from Old French rer, rere "sparse" (14c.) and directly from Latin rarus "thinly sown, having a loose texture; not thick; having intervals between, full of empty spaces" (antonym of densus). Sometimes reconstructed to be from a PIE root *ere- "to separate; adjoin."
"Having the particles not close together," hence "few in number," hence, "unusual." Sense of "remarkable from uncommonness," especially "uncommonly good" is from late 15c. (Caxton). Related: Rareness. In chemistry, rare earth is from 1818.
Rare implies that only few of the kind exist : as, perfect diamonds are rare. Scarce properly implies a previous or usual condition of greater abundance. Rare means that there are much fewer of a kind to be found than may be found where scarce would apply. [Century Dictionary, 1895]
*dhē-, Proto-Indo-European root meaning "to set, put."
It forms all or part of: abdomen; abscond; affair; affect (v.1) "make a mental impression on;" affect (v.2) "make a pretense of;" affection; amplify; anathema; antithesis; apothecary; artifact; artifice; beatific; benefice; beneficence; beneficial; benefit; bibliothec; bodega; boutique; certify; chafe; chauffeur; comfit; condiment; confection; confetti; counterfeit; deed; deem; deface; defeasance; defeat; defect; deficient; difficulty; dignify; discomfit; do (v.); doom; -dom; duma; edifice; edify; efface; effect; efficacious; efficient; epithet; facade; face; facet; facial; -facient; facile; facilitate; facsimile; fact; faction (n.1) "political party;" -faction; factitious; factitive; factor; factory; factotum; faculty; fashion; feasible; feat; feature; feckless; fetish; -fic; fordo; forfeit; -fy; gratify; hacienda; hypothecate; hypothesis; incondite; indeed; infect; justify; malefactor; malfeasance; manufacture; metathesis; misfeasance; modify; mollify; multifarious; notify; nullify; office; officinal; omnifarious; orifice; parenthesis; perfect; petrify; pluperfect; pontifex; prefect; prima facie; proficient; profit; prosthesis; prothesis; purdah; putrefy; qualify; rarefy; recondite; rectify; refectory; sacrifice; salmagundi; samadhi; satisfy; sconce; suffice; sufficient; surface; surfeit; synthesis; tay; ticking (n.); theco-; thematic; theme; thesis; verify.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit dadhati "puts, places;" Avestan dadaiti "he puts;" Old Persian ada "he made;" Hittite dai- "to place;" Greek tithenai "to put, set, place;" Latin facere "to make, do; perform; bring about;" Lithuanian dėti "to put;" Polish dziać się "to be happening;" Russian delat' "to do;" Old High German tuon, German tun, Old English don "to do."