a hair

Science Dictionary
hair   (hâr)  Pronunciation Key 


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  1. One of the fine strands that grow from the skin of mammals, usually providing insulation against the cold. Modified hairs sometimes serve as protective defenses, as in the quills of a porcupine or hedgehog, or as tactile organs, as in the whiskers (called vibrissae) of many nocturnal mammals. Hair filaments are a modification of the epidermis of the skin and are composed primarily of keratin. Hair also contains melanin, which determines hair color.

  2. A slender growth resembling a mammalian hair, found on insects and other animals.

  3. A fine, threadlike growth from the epidermis of plants. See more at trichome.


The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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