Rarefaction
Pronunciation : Rar`e*fac"tion
Part of Speech : n.
Etymology : [Cf. F. rar?faction. See Rarefy.]
Definition : Defn: The act or process of rarefying; the state of being rarefied; - - opposed to condensation; as, the rarefaction of air.
Source : Webster's Unabridged Dictionary, 1913