The Collaborative International Dictionary of English v.0.48:

Ungovernable \Un*gov"ern*a*ble\, a.
   Not governable; not capable of being governed, ruled, or
   restrained; licentious; wild; unbridled; as, ungovernable
   passions. -- Un*gov"ern*a*bly, adv. --Goldsmith.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ungovernable
    adj 1: of persons; "the little boy's parents think he is
           spirited, but his teacher finds him unruly" [syn:
           indocile, uncontrollable, ungovernable, unruly]

Moby Thesaurus II by Grady Ward, 1.0:

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