Simple Definition of immune system

from our Learner's Dictionary

immune system

noun

plural immune systems

: the system that protects your body from diseases and infections

a strong/healthy immune system

Cite this Entry

Style

“Immune system.” Merriam-Webster.com Simple Definition, Merriam-Webster, https://www.merriam-webster.com/simple/immune%20system. Accessed 20 Jun. 2026.

Copy Citation

Popular in Grammar & Usage

'Canceled' or 'cancelled'?

5 Verbal Slip Ups and Language Mistakes

Is that lie 'bald-faced' or 'bold-faced'?

'A' or 'an'? What about before 'h'? An Indefinite Article Guide

The Difference Between 'i.e.' and 'e.g.'

Popular in Wordplay

Simple Definition of immune system

immune system

noun

Cite this Entry

More from Merriam-Webster on immune system

More from Merriam-Webster

Word of the Day

longueur

Popular in Grammar & Usage

'Canceled' or 'cancelled'?

5 Verbal Slip Ups and Language Mistakes

Is that lie 'bald-faced' or 'bold-faced'?

'A' or 'an'? What about before 'h'? An Indefinite Article Guide

The Difference Between 'i.e.' and 'e.g.'

Popular in Wordplay

One-Word Oxymorons: Bittersweet, Spendthrift, and More

8 Obscure Words for Sleepy Times

Cattywampus, Taradiddle, and More Funny-Sounding Words

The Words of the Week - Jun 19

12 Lovely and Unusual Words for the Natural World

Popular

'Canceled' or 'cancelled'?

One-Word Oxymorons: Bittersweet, Spendthrift, and More

8 Obscure Words for Sleepy Times

Games & Quizzes