Definition of "mammal" []

• Any of various warm-blooded vertebrate animals of the class Mammalia, including humans, characterized by a covering of hair on the skin and, in the female, milk-producing mammary glands for nourishing the young. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "The same sort of thing was true for the term mammal in the beginning."
• "Also the term mammal contains much more definitional weight than just "anything that has hair and is endothermic" there's the whole vertebrate thing and air breathing is right up there as well as living etc etc."
• "Monotremes defy the English word mammal, which implies breasts, or at least nipples."