The Collaborative International Dictionary of English v.0.48:

Liquefy \Liq"ue*fy\ (l[i^]k"w[-e]*f[imac]), v. t. [imp. & p. p.
   Liquefied (-f[imac]d); p. pr. & vb. n. Liquefying
   (-f[imac]`[i^]ng).] [F. liqu['e]fier, L. liquere to be liquid
   + facere, -ficare (in comp.), to make. See Liquid, and
   -fy.]
   1. To convert from a solid form to that of a liquid; to melt;
      to dissolve; and technically, to melt by the sole agency
      of heat. [WordNet sense 1]
      [1913 Webster]

   2. To convert from a gaseous form into a liquid; as, to
      liquefy natural gas.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Liquefy \Liq"ue*fy\, v. i.
   To become liquid. [WordNet sense 2]
   [1913 Webster]

WordNet (r) 3.0 (2006):

liquefy
    v 1: become liquid; "The garden air overnight liquefied into a
         morning dew"
    2: make (a solid substance) liquid, as by heating; "liquefy the
       silver" [syn: liquefy, liquify, liquidize, liquidise]
    3: become liquid or fluid when heated; "the frozen fat
       liquefied" [syn: liquefy, flux, liquify]

Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "liquefy":
   colliquate, cut, decoagulate, decoct, deliquesce, dissolve,
   fluidify, fluidize, flux, fuse, hold in solution, infuse, leach,
   liquesce, liquidize, lixiviate, melt, melt down, percolate, run,
   soften, solubilize, solve, thaw, thin, unclot