The Collaborative International Dictionary of English v.0.48:

Subject-matter \Sub"ject-mat`ter\, n.
   The matter or thought presented for consideration in some
   statement or discussion; that which is made the object of
   thought or study.
   [1913 Webster]

         As to the subject-matter, words are always to be
         understood as having a regard thereto.   --Blackstone.
   [1913 Webster]

         As science makes progress in any subject-matter, poetry
         recedes from it.                         --J. H.
                                                  Newman.
   [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

SUBJECT-MATTER. The cause, the object, the thing in dispute.
     2. It is a fatal objection to the jurisdiction of the court when it has
not cognizance of the subject-matter of the action; as, if a cause
exclusively of admiralty jurisdiction were brought in a court of common law,
or a criminal proceeding in a court having jurisdiction of civil cases only.
10 Co. 68, 76 1 Ventr. 133; 8 Mass. 87; 12 Mass. 367. In such case, neither
a plea to the jurisdiction, nor any other plea would be required to oust the
court of jurisdiction. The cause might be dismissed upon motion, by the
court, ex officio.