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Meaning & use

infectious

adjective·Academic

Last updated

UK/ɪnˈfekʃəs/
US/ɪnˈfekʃəs/

Meanings

  1. adjectivenot comparable

    Describing a disease that can pass from one person, animal, or plant to another.

    Grammar: Used before a noun: an infectious disease. Not usually used after a verb.

    Patterns

    • infectious disease
    • infectious illness
    • highly infectious

    Measles is a highly infectious disease that spreads easily in crowded places.

    The doctor said the infection was no longer infectious after two days of antibiotics.

    They had to isolate the patient because the illness was still infectious.

  2. adjectivenot comparable

    Spreading quickly among people because it is exciting or easy to share.

    Grammar: Often used before a noun: infectious laughter. Can also follow a linking verb: Her enthusiasm was infectious.

    Patterns

    • infectious laughter
    • infectious enthusiasm
    • infectious smile

    Her infectious laughter made everyone in the room smile.

    The team's infectious energy kept the crowd cheering for hours.

    His excitement about the project was infectious, and soon we all wanted to help.

Common combinations

highly infectious
The virus is highly infectious and spreads through the air.
infectious disease
She specializes in treating infectious diseases.
infectious laughter
His infectious laughter filled the whole house.
infectious enthusiasm
Her infectious enthusiasm motivated the whole class.

Synonyms and how they differ

contagious
Similar for diseases spread by contact, but contagious is less often used for emotions like laughter.
catching
Informal and usually only for diseases; not used for moods or ideas.
transmissible
More technical and formal; often used in medical or scientific writing.

Opposites

noninfectious

Word family

infect verb
To pass a disease to someone or something.
infection noun
An illness caused by germs entering the body.
infectiously adverb
In a way that spreads quickly, especially laughter or enthusiasm.

Commonly confused: infectious or contagious?

infectious vs contagious

Contagious usually means spread by direct contact, while infectious can also mean spread through air or water, and is often used for emotions.

Practice

Choose the correct word: Her smile was so ___ that everyone started laughing.

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