mammal

American  

[mam-uhl] / ˈmæm əl /

noun

• mammals
  plural

1. any vertebrate of the class Mammalia, having the body more or less covered with hair, nourishing the young with milk from the mammary glands, and, with the exception of the egg-laying monotremes, giving birth to live young.

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mammal British  

/ ˈmæməl /

noun

1. any animal of the Mammalia, a large class of warm-blooded vertebrates having mammary glands in the female, a thoracic diaphragm, and a four-chambered heart. The class includes the whales, carnivores, rodents, bats, primates, etc

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mammal Scientific  

/ măm′əl /

1. Any of various warm-blooded vertebrate animals of the class Mammalia, whose young feed on milk that is produced by the mother's mammary glands. Unlike other vertebrates, mammals have a diaphragm that separates the heart and lungs from the other internal organs, red blood cells that lack a nucleus, and usually hair or fur. All mammals but the monotremes bear live young. Mammals include rodents, cats, dogs, ungulates, cetaceans, and apes.

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Other Word Forms

Derived Forms

• mammal-like
  adjective
• mammalian
  adjective
• mammallike
  adjective

Inflected Forms

Nouns

• mammals
  plural

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Etymology

Origin of mammal

First recorded in 1820–30; as singular of New Latin Mammalia, neuter plural of Late Latin mammālis “of the breast”; equivalent to mamma ² + -al ¹

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Compare meaning

How does mammal compare to similar and commonly confused words? Explore the most common comparisons:

• marsupial vs. mammal

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Explanation

What do you have in common with your hamster, a whale, a bat, a giraffe, and the kid who packs your groceries? Every one is a mammal — a hairy, warm-blooded, milk-drinking vertebrate, just like you. All mammals are part of the scientific class mammalian, which got its name from the mammary glands used to nourish mammal babies. A note of interest: although a characteristic of mammals is that babies are born live, there’s a group of mammals called monotremes, like the platypus, that lay eggs; but whose young’uns, after they hatch, still get fed mama’s milk. Go figure.

Example Sentences

See Examples For:

mammal mammals

What’s clear, according to scientists, is that it was a massive mammal that inhabited what is now Oceanside around 40 million years ago.

From Los Angeles Times ● Sep. 24, 2026

Vianna is already examining penguin genomes for genetic differences associated with survival from avian influenza, a disease currently affecting penguin, bird and mammal populations around the world.

From Science Daily ● Sep. 22, 2026

T. rex was still a scaly, egg-laying reptile, but its 36 C body temperature was much closer to that of a warm-blooded mammal than a modern reptile.

From Science Daily ● Sep. 20, 2026

The average mammal disappears from the fossil record in two million years.

From The Wall Street Journal ● Sep. 18, 2026

If anything, it stood even more upright: at the end of the long chain of adaptive evolution was the well-adjusted, best-erected, most perfected mammal of them all: humans.

From "The Gene" by Siddhartha Mukherjee

But not like us higher mammals, some of which have even become quite adept at problem-creation.

From The Wall Street Journal ● Oct. 13, 2026

It allows young mammals to consume nutrient-rich milk safely, preventing liquid from entering the nasal passages.

From Science Daily ● Oct. 13, 2026

Scientists in Australia trained sea lions and seals to respond to a hearing test for research into how the marine mammals are affected by human-made noise.

From Barron's ● Oct. 9, 2026

It’s caused by a bacteria called Yersinia pestis that infects fleas and the small mammals that host fleas, and there are actually three types of plague depending on which part of the body becomes infected.

From Slate ● Oct. 8, 2026

We were from different groups, our own version of mammals, reptiles, and fish.

From "Auggie & Me" by R. J. Palacio

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Related Words

• beast
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