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, 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

Derived Forms

• mammal-like
  adjective
• mammalian
  adjective
• mammallike
  adjective

Inflected Forms

Nouns

• mammals
  plural

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

To combat this, the Shropshire Mammal Group has been tracking the endangered species using the boxes, funded by a £1,500 grant from Shropshire Hills National Landscape.

From BBC • May 19, 2026

Chonkers is a Steller, a different species from his dockmates, according to Laura Gill, public programs manager with Marine Mammal Center.

From The Wall Street Journal • Apr. 26, 2026

The sea lion breeding and pupping season is fast approaching at main rookeries such as the Channel Islands, according to Giancarlo Rulli, associate director of public relations for the Marine Mammal Center.

From Los Angeles Times • Apr. 9, 2026

One key factor may be the Marine Mammal Protection Act of 1972, which helped populations of seals, sea lions, orcas, and other marine mammals recover after years of decline.

From Science Daily • Apr. 1, 2026

“It predicted what might happen to the seal population off Cape Cod after the Marine Mammal Protection Act became law. Back then, seals had been my focus.”

From "The Line Tender" by Kate Allen

Related Words

• beast
• creature
• vertebrate