Source : Webster's Revised Unabridged Dictionary (1913)

Assertive \As*sert"ive\, a.
   Positive; affirming confidently; affirmative; peremptory.

         In a confident and assertive form.       --Glanvill.
   {As*sert"ive*ly}, adv. -- {As*sert"ive*ness}, n.

Source : WordNet®

assertiveness
     n : aggressive self-assurance; given to making bold assertions
         [syn: {self-assertiveness}]