Infectious means able to be spread by infection, like a disease that spreads from one person to another. You'll be uncomfortable shaking Uncle Marvin's hand if you're worried that warts are infectious.

Something that's infectious spreads easily, like infectious cold germs that might be left on a door handle — anyone who touches it might get sick. If your mother tells you the cut on your knee looks infectious, you'd better go to the doctor. Some infectious things are good — like infectious laughter that gets the whole class giggling, or your friend's infectious good mood that makes you forget your cares.

Definitions of infectious

adj of or relating to infection

infectious hospital”
infectious disease”

adj caused by infection or capable of causing infection

infected, septic
containing or resulting from disease-causing organisms

adj easily spread

“fear is exceedingly infectious
catching, communicable, contagious, contractable, transmissible, transmittable
(of disease) capable of being transmitted by infection
easily diffused or spread as from one person to another
contaminating, corrupting
that infects or taints
not infectious
noncommunicable, noncontagious, nontransmissible
(of disease) not capable of being passed on
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