deliquesce

verb2

1. •
   To melt by absorbing water and disappearing.

   • But I could find no saltpetre; indeed, no nitrates of any kind. Doubtless they had deliquesced ages ago. — 1895
2. •
   To become liquid by absorbing water from the atmosphere and dissolving in it.

   • Some salts will deliquesce when left exposed.