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

A particularly massive sea lion has Bay Area tourists and residents flocking to Pier 39 in San Francisco to spot the mammal affectionately named “Chonkers.”

From Los Angeles Times • Apr. 30, 2026

It finally answers a long-standing question about early mammal evolution.

From Science Daily • Apr. 14, 2026

The discovery provides the first direct evidence that mammal ancestors laid eggs and also helps explain why Lystrosaurus became so successful in post-extinction ecosystems.

From Science Daily • Apr. 14, 2026

But such an old mammal bone was the last thing he and his daughter had expected to discover.

From BBC • Apr. 10, 2026

It was the first time any human had managed to leave the Afro-Asian ecological system—indeed, the first time any large terrestrial mammal had managed to cross from Afro-Asia to Australia.

From "Sapiens: A Brief History of Humankind" by Yuval Noah Harari

Related Words

• beast
• creature
• vertebrate