- 1an infectious disease can be passed easily from one person to another, especially through the air they breathe The flu is highly infectious. (figurative) infectious laughter
- 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. compare contagious
adverb to laugh infectiously
noun [uncountable]See infectious in the Oxford Advanced Learner's Dictionary
Check pronunciation: infectious