Source : Webster's Revised Unabridged Dictionary (1913)

Subclass \Sub"class`\, n.
   One of the natural groups, more important than an order, into
   which some classes are divided; as, the angiospermous
   subclass of exogens.

Source : WordNet®

subclass
     n : (biology) a taxonomic category below a class and above an
         order

Source : Free On-Line Dictionary of Computing

subclass
     
        {derived class}