rarefy

rar·e·fy also rar·i·fy  (râr-f)

v. rar·e·fied, rar·e·fy·ing, rar·e·fies

v.tr.

1. To make thin, less compact, or less dense.

2. To purify or refine.

v.intr.

To become thin or less compact or dense.

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[Middle English rarefien, from Old French rarefier, from Medieval Latin rrificre, alteration of Latin rrfacere : rrus, rare + facere, to make; see dh- in Indo-European roots.]

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rare·fia·ble adj.

Thesaurus

Verb	1.	rarefy - lessen the density or solidity of; "The bones are rarefied" alter, change, modify - cause to change; make different; cause a transformation; "The advent of the automobile may have altered the growth pattern of the city"; "The discussion has changed my thinking about the issue"
	2.	rarefy - make more subtle or refined sublimate, subtilize alter, change, modify - cause to change; make different; cause a transformation; "The advent of the automobile may have altered the growth pattern of the city"; "The discussion has changed my thinking about the issue"
	3.	rarefy - weaken the consistency of (a chemical substance) attenuate chemical science, chemistry - the science of matter; the branch of the natural sciences dealing with the composition of substances and their properties and reactions weaken - lessen the strength of; "The fever weakened his body"