in ‧ fec ‧ tious /ɪnˈfekʃəs/ BrE AmE adjective
[ Word Family: noun : ↑ infection , ↑ disinfectant ; adjective : ↑ infectious , ↑ infected ; verb : ↑ infect ≠ ↑ disinfect ; adverb : ↑ infectiously ]
1 . an infectious illness can be passed from one person to another, especially through the air you breathe:
infectious diseases
Flu is highly infectious.
2 . someone who is infectious has an illness and could pass it to other people
3 . infectious feelings or laughter spread quickly from one person to another:
an infectious smile
infectious enthusiasm
—infectiously adverb