infectious

adjective in·fec·tious \ in-ˈfek-shəs \
|Updated on: 24 Jun 2018

Definition of infectious

1 a : capable of causing infection
  • viruses and other infectious agents
b : communicable by infection
  • an infectious disease
— compare contagious
2 : that corrupts or contaminates
3 : spreading or capable of spreading rapidly to others
  • their enthusiasm was infectious
  • an infectious grin

infectiously

adverb

infectiousness

noun

Examples of infectious in a Sentence

  1. viruses and other infectious agents

  2. She has an infectious grin.

Recent Examples of infectious from the Web

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'infectious.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

What is the Difference Between contagious and infectious?

The words contagious and infectious can be confusing because they do not designate wholly distinct categories; something is not either contagious or infectious.

Essentially, infectious diseases and contagious diseases are caused by disease-producing agents such as bacteria and viruses, but they differ in that contagious diseases can be spread to other people by direct or indirect contact.

Anything contagious, such as the flu, is always automatically infectious: if you can catch it from someone, it's being passed to you via an infectious agent, which is the thing that gets you sick—usually a virus or a bacteria.

The reverse, however, isn't true. Just because something is infectious does not mean it's contagious. Food poisoning, for example, is infectious but not contagious: food can be contaminated with a bacteria (an infectious agent) that makes you sick, but you can't give your food poisoning to someone else by shaking their hand or even giving them a kiss.

Both contagious and infectious are also used figuratively, often in much happier contexts: laughter can be contagious; someone's enthusiasm can be infectious. While both words are used figuratively of both pleasant and unpleasant things, contagious is more often chosen for the unpleasant, as when it's grumpiness or fear that seems to be spreading.

First Known Use of infectious

1534

in the meaning defined at sense 1a

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INFECTIOUS Defined for English Language Learners

infectious

Definition of infectious for English Language Learners

  • : capable of causing infection

  • : capable of being passed to someone else by germs that enter the body

  • : suffering from a disease that can be spread to other people by germs


INFECTIOUS Defined for Kids

infectious

adjective in·fec·tious \ in-ˈfek-shəs \

Definition of infectious for Students

1 : passing from one to another in the form of a germ
  • an infectious illness
2 : easily spread to others
  • an infectious laugh

Medical Dictionary

infectious

adjective in·fec·tious \ in-ˈfek-shəs \

medical Definition of infectious

1 : capable of causing infection
  • a carrier remains infectious without exhibiting signs of disease
  • viruses and other infectious agents
2 : communicable by invasion of the body of a susceptible organism
  • all contagious diseases are also infectious, but it does not follow that all infectious diseases are contagious
  • —W. A. Hagan
— compare contagious 1

infectiously

adverb

infectiousness

noun


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