: any of a class (Mammalia) of warm-blooded higher vertebrates (such as placentals, marsupials, or monotremes) that nourish their young with milk secreted by mammary glands, have the skin usually more or less covered with hair, and include humans
mammal-like
adjective
or less commonly mammallike
mammal-like behavior
mammallike reptiles
Examples of mammal in a Sentence
Human beings, dogs, and cats are all mammals.
Recent Examples on the Web
The same designs may also support therapies for marine mammals.
—
Aamir Khollam, Interesting Engineering, 19 Sep. 2025
However, the techniques necessary to bring back a bird such as the dodo are different from those the company used to create dire wolves because birds develop in an egg and can’t be cloned in the same way as mammals, making the process more challenging.
—Katie Hunt, CNN Money, 17 Sep. 2025
Other mammals, including elephants and tree shrews, and some birds, such as Cedar Waxwings and hummingbirds, eat fermented fruit and nectar, which contain ethanol.
—Kate Wong, Scientific American, 17 Sep. 2025
Evolution has adapted the digits of mammals for an enormous range of uses, from our opposable thumbs to the spindly digits that support bat wings to the robust bones that support the hoofs of horses.
—John Timmer, ArsTechnica, 17 Sep. 2025
See All Example Sentences for mammal
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Aamir Khollam, Interesting Engineering, 19 Sep. 2025
However, the techniques necessary to bring back a bird such as the dodo are different from those the company used to create dire wolves because birds develop in an egg and can’t be cloned in the same way as mammals, making the process more challenging.
—Katie Hunt, CNN Money, 17 Sep. 2025
Other mammals, including elephants and tree shrews, and some birds, such as Cedar Waxwings and hummingbirds, eat fermented fruit and nectar, which contain ethanol.
—Kate Wong, Scientific American, 17 Sep. 2025
Evolution has adapted the digits of mammals for an enormous range of uses, from our opposable thumbs to the spindly digits that support bat wings to the robust bones that support the hoofs of horses.
—John Timmer, ArsTechnica, 17 Sep. 2025
See All Example Sentences for mammal
Cite this Entry
“Mammal.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/mammal. Accessed 20 Sep. 2025.
Copy CitationKids Definition
mammal
noun
mam·mal
ˈmam-əl 
: any of a class of warm-blooded vertebrates that include human beings and all other animals that nourish their young with milk produced by mammary glands and have the skin usually more or less covered with hair
Medical Definition
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