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]