The Collaborative International Dictionary of English v.0.48:

Superfamily \Su"per*fam`i*ly\, n. (Zool.)
   A group intermediate between a family and a suborder.
   [1913 Webster]

WordNet (r) 3.0 (2006):

superfamily
    n 1: (biology) a taxonomic group ranking below an order but
         above a family