The Collaborative International Dictionary of English v.0.48:

Aggressive \Ag*gres"sive\, a. [Cf. F. agressif.]
   1. Tending or disposed to aggress; having or showing
      determination and energetic pursuit of one's own ends at
      the expense of others or mindless of others' needs or
      desires; characterized by aggression; making assaults;
      unjustly attacking; as, an aggressive policy, war, person,
      nation; an aggressive businessman; an aggressive
      basketball player; he was aggressive and imperious in his
      convictions; aggressive drivers. Opposite of
      unaggressive.
      [1913 Webster + WordNet 1.5]

            No aggressive movement was made.      --Macaulay.
      [1913 Webster]

   2. Marked by self-confident ambition, vigorous
      competitiveness, energy and initiative; as, an aggressive
      young executive.

   Syn: enterprising, pushful, pushing, pushy
        [WordNet 1.5]

   3. (Med., Biol.) Tending to grow or spread quickly; as, an
      aggressive tumor. [Narrower terms: invasive (vs.
      noninvasive) ] --AS

   Syn: fast-growing(prenominal)
        [WordNet 1.5]

   4. Tending to initiate unprovoked attacks; initiating
      unprovoked military action; eager to fight; as, aggressive
      acts against another country.

   Syn: belligerent.
        [WordNet 1.5]

   Note: Narrower related terms: {bellicose, combative,
         pugnacious, scrappy, truculent ; {hard-hitting,
         high-pressure ; {hostile (used of attempts to buy or
         take control of a business: "hostile takeover";
         "hostile tender offer"); predatory, rapacious,
         raptorial, ravening, vulturine, vulturous . See also:
         assertive, hostile, offensive.
         [WordNet 1.5] -- {Ag*gres"sive*ly, adv. --
         Ag*gres"sive*ness, n.
         [1913 Webster]

WordNet (r) 3.0 (2006):

aggressively
    adv 1: in an aggressive manner; "she was being sharply
           questioned" [syn: aggressively, sharply]