hair is any of the cylindrical filaments characteristically growing from the epidermis of a mammal
Here's the official definition:
1. any of the numerous fine, usually cylindrical, keratinous filaments growing from the skin of humans and animals; a pilus.
2. an aggregate of such filaments, as that covering the human head or forming the coat of most mammals.
3. a similar fine, filamentous outgrowth from the body of insects, spiders, etc.
4. Botany . a filamentous outgrowth of the epidermis.
5. cloth made of hair from animals, as camel and alpaca.
before 900; Middle English heer, Old English hǣr (cognate with Dutch, German haar, Old Norse hār ), with vowel perhaps from Middle English haire hair shirt < Old French < Old High German hāria (cognate with Middle English here, Old English hǣre, Old Norse hǣra )