The Collaborative International Dictionary of English v.0.48:

Mongrel \Mon"grel\, n. [Prob. shortened fr. mongrel, and akin to
   AS. mengan to mix, and E. mingle. See Mingle.]
   The progeny resulting from a cross between two breeds, as of
   domestic animals; anything of mixed breed. --Drayton.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Mongrel \Mon"grel\, a.
   1. (Zool.) Not of a pure breed.
      [1913 Webster]

   2. Of mixed kinds; as, mongrel language.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mongrel
    n 1: derogatory term for a variation that is not genuine;
         something irregular or inferior or of dubious origin; "the
         architecture was a kind of bastard suggesting Gothic but
         not true Gothic" [syn: bastard, mongrel]
    2: an inferior dog or one of mixed breed [syn: cur, mongrel,
       mutt]