The Collaborative International Dictionary of English v.0.48:

Deliquesce \Del`i*quesce"\, v. i. [imp. & p. p. Deliquesced;
   p. pr. & vb. n. Deliquescing.] [L. deliquescere to melt,
   dissolve; de- + liquescere to become fluid, melt, fr. liquere
   to be fluid. See Liquid.] (Chem.)
   To dissolve gradually and become liquid by attracting and
   absorbing moisture from the air, as certain salts, acids, and
   alkalies.

         In very moist air crystals of strontites deliquesce.
                                                  --Black.
   [1913 Webster]

WordNet (r) 3.0 (2006):

deliquesce
    v 1: melt away in the process of decay; "The fungi eventually
         deliquesced"
    2: melt or become liquid by absorbing moisture from the air;
       "this type of salt deliquesces easily"