infectious

adjective in·fec·tious \ in-ˈfek-shəs \
Updated on: 14 Nov 2017

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.

First Known Use of infectious

1534


INFECTIOUS Defined for English Language Learners

infectious

adjective

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


Seen and Heard

What made you want to look up infectious? Please tell us where you read or heard it (including the quote, if possible).

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

WORD OF THE DAY

to remove or wipe out

Get Word of the Day daily email!

Test Your Vocabulary

Find the Cousins

  • a-large-tree-with-many-branches
  • Which pair shares a common word ancestor?
True or False

Test your knowledge - and maybe learn something along the way.

TAKE THE QUIZ
Word Winder's CrossWinder

Test Your Knowledge - and learn some interesting things along the way.

TAKE THE QUIZ

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!