infectious

From infect +‎ -ious.

• (General American, Received Pronunciation) IPA^(key): /ɪnˈfɛk.ʃəs/

• Audio (Canada):

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infectious (comparative more infectious, superlative most infectious)

1. (pathology, of an illness) 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. (pathology, typically of a person) Able to infect others; capable of transmitting pathogens.

   Despite feeling better, the patient is still infectious.

   • 1981 December 1, Sue Hyde, quoting Paul Black, “AIDS Update: Little To Cheer About”, in Gay Community News, volume 12, number 20, page 3:

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

3. (of feelings and behaviour) Spreading quickly from one person to another.

   Her enthusiasm for work can be really infectious.

   • 2024 November 20, Fortesa Latifi, “How These Men Left the Manosphere — and Why Some May Never”, in Teen Vogue‎^[1]:

     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.

The terms infectious, communicable, transmissible/transmittable, and contagious, as well as spreadable and catching, overlap on a semantic field and are often loosely used synonymously in their broad senses, although they are differentiable by narrower senses, as follows:

• The word infectious describes any disease or condition that is caused by an infectious agent (such as a bacterium, virus, parasite, or prion), including ones with person-to-person transmission/spread and ones without person-to-person transmission/spread. It is thus hypernymous to the following terms.
• The words communicable and transmissible/transmittable, as well as spreadable and catching (which are informal), describe the large subset of infectious diseases in which person-to-person transmission/spread (communication) can occur, including ones that are readily/easily spread and ones that are not readily/easily spread. They are thus hypernymous to the following term.
• The word contagious describes only those infectious diseases that are readily/easily spread, to the degree that preventing their spread is quite difficult unless a population is highly vaccinated against them (examples include measles and diphtheria).

See Usage notes.

• non-infectious, noninfectious (which are hypernymous to noncommunicable)

• countifies