The Collaborative International Dictionary of English v.0.48:

Muriate \Mu"ri*ate\, n. [See Muriatic.] (Chem.)
   A salt of muriatic hydrochloric acid; a chloride; as, muriate
   of ammonia.
   [1913 Webster]

   Note: This term, as also the word muriatic, was formerly
         applied to the chlorides before their true composition
         was understood, and while they were erroneously
         supposed to be compounds of an acid with an oxide.
         Muriate and muriatic are still occasionally used as
         commercial terms, but are obsolete in scientific
         language.
         [1913 Webster]