The Collaborative International Dictionary of English v.0.48:

Liquefaction \Liq`ue*fac"tion\ (l[i^]k`w[-e]*f[a^]k"sh[u^]n), n.
   [L. liquefactio: cf. F. liqu['e]faction. See Liquefy.]
   1. The act or operation of making or becoming liquid;
      especially, the conversion of a solid into a liquid by the
      sole agency of heat.
      [1913 Webster]

   2. The state of being liquid.
      [1913 Webster]

   3. (Chem. Physics) The act, process, or method, of reducing a
      gas or vapor to a liquid by means of cold or pressure; as,
      the liquefaction of oxygen or hydrogen.
      [1913 Webster]

WordNet (r) 3.0 (2006):

liquefaction
    n 1: the conversion of a solid or a gas into a liquid

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "liquefaction":
   chylifaction, chylification, flow, fluency, fluidity, fluidness,
   flux, fluxility, fluxion, juiciness, lactation, lactescence,
   liquidness, milkiness, moisture, rheuminess, sappiness, serosity,
   succulence, suppuration, wateriness