The Collaborative International Dictionary of English v.0.48:

Impact \Im*pact"\, v. t. [imp. & p. p. Impacted; p. pr. & vb.
   n. Impacting.] [L. impactus, p. p. of impingere to push,
   strike against. See Impinge.]
   1. To drive close; to press firmly together: to wedge into a
      place. --Woodward.
      [1913 Webster]

   2. To affect or influence, especially in a significant or
      undesirable manner; as, budget cuts impacted the entire
      research program; the fish populations were adversely
      impacted by pollution.
      [PJC]

   3. To collide forcefully with; to strike.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Impacted \Im*pact"ed\, a.
   1. Driven together or close.
      [1913 Webster]

   2. Specifically: (Dentistry) Grown in an abnormal direction
      so that it is wedged against another tooth and cannot
      erupt normally; -- of teeth, especially the third molar;
      as, to extract an impacted third molar.
      [PJC]

   Impacted fracture (Surg.), a fracture in which the
      fragments are driven into each other so as to be
      immovable.
      [1913 Webster]

WordNet (r) 3.0 (2006):

impacted
    adj 1: wedged or packed in together; "an impacted tooth" [syn:
           impacted, wedged]