Source : Webster's Revised Unabridged Dictionary (1913)

Argillaceous \Ar`gil*la"ceous\, a. [L. argillaceus, fr.
   argilla.]
   Of the nature of clay; consisting of, or containing, argil or
   clay; clayey.

   {Argillaceous sandstone} (Geol.), a sandstone containing much
      clay.

   {Argillaceous iron ore}, the clay ironstone.

   {Argillaceous schist} or {state}. See {Argillite}.

Source : WordNet®

argillaceous
     adj : resembling or containing clay; "argillaceous rocks" [syn: {clayey}]
           [ant: {arenaceous}]