THESAURUS
Rarefy
add to, adulterate, aggrandize, amplify, attenuate, augment, baptize, bloat, blow up, broaden, build, build up, bulk, bulk out, crescendo, cut, dematerialize, develop, dilate, dilute, disembody, distend, emacerate, emaciate, enervate, enlarge, etherealize, expand, extend, hike, hike up, huff, increase, inflate, irrigate, magnify, puff, puff up, pump, pump up, raise, reduce, sap, spiritualize, stretch, subtilize, sufflate, swell, thin, thin away, thin down, thin out, up, water, water down, weaken, widen
ROGET THESAURUS
Rarefy
Expansion
VB
become larger &c (large), expand, widen, enlarge, extend, grow, increase, incrassate, swell, gather, fill out, deploy, take open order, dilate, stretch, distend, spread, mantle, wax, grow up, spring up, bud, bourgeon, shoot, sprout, germinate, put forth, vegetate, pullulate, open, burst forth, gain flesh, gather flesh, outgrow, spread like wildfire, overrun, be larger than, surpass, render larger &c (large), expand, spread, extend, aggrandize, distend, develop, amplify, spread out, widen, magnify, rarefy, inflate, puff, blow up, stuff, pad, cram, exaggerate, fatten.
Rarity
VB
rarefy, expand, dilate, subtilize.