The Collaborative International Dictionary of English v.0.48:

Aggress \Ag*gress"\, v. i. [imp. & p. p. Aggressed; p. pr. &
   vb. n. Aggressing.] [L. aggressus, p. p. of aggredi to go
   to, approach; ad + gradi to step, go, gradus step: cf. OF.
   aggresser. See Grade.]
   To commit the first act of hostility or offense; to begin a
   quarrel or controversy; to make an attack; -- with on.
   [1913 Webster]

   2. take the initiative and go on the offensive, as in a game.

   Syn: attack
        [WordNet 1.5]