The Collaborative International Dictionary of English v.0.48:

Insuppressible \In`sup*press"i*ble\, a.
   That can not be suppressed or concealed; irrepressible.
   --Young. -- In`sup*press"i*bly, adv.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

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