mammal

American  

[mam-uhl] / ˈmæm əl /

noun

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, mæˈmeɪlɪən /

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

• mammal-like adjective
• mammalian adjective
• mammallike adjective

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

Compare meaning

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

• marsupial vs. mammal

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

The juvenile whale, affectionately dubbed "Willapa Willy" by locals, was first spotted last Wednesday in the north fork of the river, about 145 miles southwest of Seattle, the marine mammal research group said.

From BBC • Apr. 6, 2026

The marine mammal, which is stuck on a sandbank, was first spotted in Lübeck Bay on Monday.

From BBC • Mar. 26, 2026

Purgatorius, a small mammal about the size of a shrew, appears in the fossil record shortly after the dinosaurs went extinct around 65.9 million years ago.

From Science Daily • Mar. 3, 2026

It’s not exactly a chicken and dinosaur-egg question, but which came first, the mammal or the giant lizard?

From The Wall Street Journal • Feb. 10, 2026

Those Major Five of mammal domestication are the cow, sheep, goat, pig, and horse.

From "Guns, Germs, and Steel: The Fates of Human Societies" by Jared M. Diamond

Related Words

• beast
• creature
• vertebrate