The Collaborative International Dictionary of English v.0.48:
Assertive \As*sert"ive\, a. Positive; affirming confidently; affirmative; peremptory. [1913 Webster] In a confident and assertive form. --Glanvill. [1913 Webster] As*sert"ive*ly, adv. -- As*sert"ive*ness, n. [1913 Webster]WordNet (r) 3.0 (2006):
assertiveness n 1: aggressive self-assurance; given to making bold assertions [syn: assertiveness, self-assertiveness]