The Collaborative International Dictionary of English v.0.48:

Undifferentiated \Un*dif`fer*en"ti*a`ted\, a.
   Not differentiated; specifically (Biol.), homogenous, or
   nearly so; -- said especially of young or embryonic tissues
   which have not yet undergone differentiation (see
   Differentiation, 3), that is, which show no visible
   separation into their different structural parts.
   [1913 Webster]

WordNet (r) 3.0 (2006):

undifferentiated
    adj 1: not differentiated [syn: undifferentiated, uniform]
           [ant: differentiated]