1.AdjectiveCaused 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.AdjectiveAble to infect others; capable of transmitting pathogens.
"Despite feeling better, the patient is still infectious."
3.AdjectiveSpreading quickly from one person to another.
"infectious smile; Her enthusiasm for work can be really infectious."
4.AdjectiveMemorable and invoking excitement or interest.
"Pop music is more infectious than elevator music."