invasion in WordNet English dictionary

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