The Collaborative International Dictionary of English v.0.48:

neanderthal \neanderthal\ adj.
   1. uncouth in manners or appearance.

   Syn: boorish, clownish, loutish, oafish.
        [WordNet 1.5] Neanderthal race
        Neanderthal

The Collaborative International Dictionary of English v.0.48:

Neanderthal \Ne*an"der*thal`\, prop. a.
   1. (Anthropol.) Of, pertaining to, or named from, the
      Neanderthal, a valley in the Rhine Province, in which were
      found parts of a skeleton of an early type of man. The
      skull is characterized by extreme dolichocephaly, flat,
      retreating forehead, with closed frontal sutures, and
      enormous superciliary ridges. The cranial capacity is
      estimated at about 1,220 cubic centimeters, being about
      midway between that of the Pithecanthropus and modern
      man. Hence, pertaining to or designating the

The Collaborative International Dictionary of English v.0.48:

Neanderthal \Ne*an"der*thal`\, prop. n.
   1. (Anthropol.) A neanderthal human being; a member of the
      race Homo sapiens neanderthalensis; as, neanderthals
      were shorter than modern humans.
      [PJC]

   2. One resembling a neanderthal human; a troglodyte; a cave
      man.
      [PJC]

   3. Hence: (Fig.) A person of primitive, unenlightened or
      uneducated opinions or attitudes; one with a regressive
      social or political outlook; -- used disparagingly.
      [PJC]

WordNet (r) 3.0 (2006):

neanderthal
    adj 1: ill-mannered and coarse and contemptible in behavior or
           appearance; "was boorish and insensitive"; "the loutish
           manners of a bully"; "her stupid oafish husband";
           "aristocratic contempt for the swinish multitude" [syn:
           boorish, loutish, neanderthal, neandertal,
           oafish, swinish]
    2: relating to or belonging to or resembling Neanderthal man;
       "Neanderthal skull" [syn: Neanderthal, Neanderthalian,
       Neandertal]
    n 1: extinct robust human of Middle Paleolithic in Europe and
         western Asia [syn: Neandertal man, Neanderthal man,
         Neandertal, Neanderthal, Homo sapiens
         neanderthalensis]

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "Neanderthal":
   Goth, Gothic, animal, barbarian, barbaric, barbarous, bestial,
   brutal, brute, brutish, ill-bred, impolite, noncivilized,
   outlandish, primitive, rough-and-ready, savage, troglodyte,
   troglodytic, uncivil, uncivilized, uncombed, uncouth, uncultivated,
   uncultured, unkempt, unlicked, unpolished, unrefined, untamed,
   wild