Definition of mammal in US English:



  • A warm-blooded vertebrate animal of a class that is distinguished by the possession of hair or fur, the secretion of milk by females for the nourishment of the young, and (typically) the birth of live young.

    The first small mammals evolved from reptiles about 200 million years ago, and the group diversified rapidly after the extinction of the dinosaurs to become the dominant form of land animal, with about 4,000 living species. Mammals belong to the class Mammalia, which contains the subclass Prototheria (monotremes) and the infraclasses Metatheria (marsupials) and Eutheria (placental mammals such as rodents, cats, whales, bats, and humans)

    • ‘The male feeds the female while she incubates, catching small mammals and birds and bringing them back to the nest.’
    • ‘The sloths and armadillos are rather odd mammals characteristic of South America.’
    • ‘West Nile Virus is found mainly in birds, though it is also found in horses and other mammals.’
    • ‘Nothing is more remarkable than the effects of habit in herbivorous mammals.’
    • ‘The domestic animal is the first mammal known to die of the disease in Europe.’
    • ‘The decaying wood also becomes home to a range of insects and small mammals.’
    • ‘They inhabited a world that was dominated by a different kind of animal - the mammal.’
    • ‘Some mammals can distinguish between and respond to the alarm calls of other mammal and bird species.’
    • ‘Animal pathologists found the mammals had suffered internal bleeding in the ears and the brain.’
    • ‘The teeth and their pattern of wear are unlike that seen in any modern mammal so what this animal ate is something of a mystery.’
    • ‘Certainly, a lot of changes would have to occur for a land mammal to live in the sea.’
    • ‘The island refuges of some species are also under threat from imported mammals such as rats and hedgehogs.’
    • ‘Unlike mammals, chicks do not feed on milk formula as their stomachs cannot digest it.’
    • ‘This bulky animal is one of the most dangerous mammals to be found anywhere.’
    • ‘It provides the growing young with everything it wants, and only mammals produce milk.’
    • ‘Dolphins are mammals and as such are warm-blooded and bear live young, which they suckle.’
    • ‘Their prey consists mainly of birds and small mammals such as rats and agoutis.’
    • ‘Recently, the rat became the third mammal for which the complete genome was sequenced.’
    • ‘The lack of suitable nest sites has also resulted in increased predation by corvids and mammals on the eggs and chicks.’
    • ‘The domes will contain different freshwater environments containing fish and aquatic mammals.’


Early 19th century: anglicized form (first used in the plural) of modern Latin mammalia, neuter plural of Latin mammalis (adjective), from mamma ‘breast’ (see mamma).