Definition of infectious adjective from the Oxford Advanced Learner's Dictionary

      

    infectious

     adjective
    adjective
    BrE BrE//ɪnˈfekʃəs//
     
    ; NAmE NAmE//ɪnˈfekʃəs//
     
    Ailments and diseases, Being ill
     
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  1. 1  an infectious disease can be passed easily from one person to another, especially through the air they breathe Flu is highly infectious. (figurative) infectious laughter
  2. 2  [not usually before noun] if a person or an animal is infectious, they have a disease that can be spread to others I'm still infectious. See related entries: Ailments and diseases, Being ill
  3. compare contagious
    Word Origin mid 16th cent.: from infection + -ous.
See the Oxford Advanced American Dictionary entry: infectious