The Collaborative International Dictionary of English v.0.48:

Untamable \Untamable\
   See tamable.

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "untamable":
   beyond control, breachy, contumacious, defiant, fractious,
   incorrigible, indocile, indomitable, insuppressible, intractable,
   irrepressible, obstreperous, out of hand, recalcitrant, refractory,
   resistant, resisting, restive, shrewish, unbiddable,
   uncontrollable, ungovernable, unmalleable, unmanageable,
   unmoldable, unruly, unsubmissive, wild