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]

Moby Thesaurus II by Grady Ward, 1.0:

143 Moby Thesaurus words for "undifferentiated":
   abstract, accordant, agnate, akin, alike, analogous, articulated,
   austere, automatic, balanced, bare, basic, bland, broad, catenated,
   ceaseless, chaste, collective, comparable, concatenated, connected,
   consistent, consonant, constant, continual, continued, continuing,
   continuous, correspondent, corresponding, cyclical, direct,
   elementary, endless, equable, equal, essential, even, featureless,
   flat, fundamental, gapless, general, generalized, generic, homely,
   homespun, homogeneous, immediate, immutable, incessant, indefinite,
   indeterminate, indiscernible, indistinct, indistinctive,
   indistinguishable, indivisible, interchangeable, interminable,
   invariable, irreducible, joined, jointless, level, linked,
   measured, mechanical, mere, methodic, monolithic, monotonous,
   nebulous, neutral, never-ending, nonspecific, nonstop, of a piece,
   ordered, orderly, parallel, perennial, periodic, persistent, plain,
   primal, primary, pure, pure and simple, recurrent, regular,
   repetitive, robotlike, round-the-clock, running, seamless, serried,
   severe, similar, simon-pure, simple, single, smooth, spare, stable,
   standard, stark, steadfast, steady, stereotyped, straight,
   systematic, twenty-four-hour, unadorned, unbroken, unceasing,
   unchangeable, unchanged, unchanging, uncharacterized, uncluttered,
   undeviating, undifferenced, undiscriminated, undistinguishable,
   undistinguished, undiversified, unending, uniform, unintermitted,
   unintermittent, unintermitting, uninterrupted, unrelieved,
   unremitting, unruffled, unspecified, unstopped, unvaried,
   unvarying, vague, wide, without distinction