infectious in WordNet English dictionary

1. easily spread
   "fear is exceedingly infectious; children catch it from their elders"- Bertrand Russell
   infectious 
   
2. of or relating to infection
   "infectious hospital"; "infectious disease"
   infectious 
   
3. caused by infection or capable of causing infection
   "viruses and other infective agents"; "a carrier remains infective without himself showing signs of the disease"
   infectious  infective