Source : Webster's Revised Unabridged Dictionary (1913)

Headstrong \Head"strong`\ (?; 115), a.
   1. Not easily restrained; ungovernable; obstinate; stubborn.

            Not let headstrong boy my will control. --Dryden.

   2. Directed by ungovernable will, or proceeding from
      obstinacy. --Dryden.

   Syn: Violent; obstinate; ungovernable; unratable; stubborn;
        unruly; venturesome; heady.

Source : WordNet®

headstrong
     adj : habitually disposed to disobedience and opposition [syn: {froward},
            {self-willed}, {willful}, {wilful}]