Hypertext Webster Gateway: "rarefaction"
From Webster's Revised Unabridged Dictionary (1913) (web1913)
Rarefaction \Rar`e*fac"tion\, n. [Cf. F. rar['e]faction. See
{Rarefy}.]
The act or process of rarefying; the state of being rarefied;
-- opposed to condensation; as, the rarefaction of air.
From WordNet (r) 1.7 (wn)
rarefaction
n : a decrease in the density of something; "a sound wave causes
periodic rarefactions in its medium"
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