invasion
    n 1: the act of invading; the act of an army that invades for
         conquest or plunder
    2: any entry into an area not previously occupied; "an invasion
       of tourists"; "an invasion of locusts" [syn: invasion,
       encroachment, intrusion]
    3: (pathology) the spread of pathogenic microorganisms or
       malignant cells to new sites in the body; "the tumor's
       invasion of surrounding structures"

Invasion \In*va"sion\, n. [L. invasio: cf. F. invasion. See
   Invade.]
   [1913 Webster]
   1. The act of invading; the act of encroaching upon the
      rights or possessions of another; encroachment; trespass.
      [1913 Webster]

   2. A warlike or hostile entrance into the possessions or
      domains of another; the incursion of an army for conquest
      or plunder.
      [1913 Webster]

   3. The incoming or first attack of anything hurtful or
      pernicious; as, the invasion of a disease.

   Syn: Invasion, Irruption, Inroad.

   Usage: Invasion is the generic term, denoting a forcible
          entrance into a foreign country. Incursion signifies a
          hasty and sudden invasion. Irruption denotes
          particularly violent invasion. Inroad is entry by some
          unusual way involving trespass and injury.
          [1913 Webster]

INVASION. The entry of a country by a public enemy, making war. 
     2. The Constitution of the United States, art. 1, s. 8, gives power to 
congress "to provide for calling the militia to execute the laws of the 
Union, suppress insurrections, and repel invasions." Vide Insurrection.