infectious

adj

1. Caused by an agent that enters the host's body (such as a bacterium, virus, parasite, or prion); often, also, transmitted among hosts via any of various routes (for example, contact, droplet-borne, airborne, waterborne, foodborne, fomite-borne, or bloodborne).

   “Cancer is usually not infectious.”

   “More infectious diseases like the flu are usually less potent.”

2. Able to infect others; capable of transmitting pathogens.

   “Despite feeling better, the patient is still infectious.”

   “I doubt that [saliva] is very infectious ... I don't think this is a normal route of transmission.”

3. Spreading quickly from one person to another.

   “infectious smile”

   “Her enthusiasm for work can be really infectious.”

   “When Maisie first met Danny, she remembers that he had an infectious laugh and a love for music.”

4. (informal)Memorable and invoking excitement or interest.

   “Pop music is more infectious than elevator music.”