hair: the fine threadlike growth on the head or body of a person or animal, or a single strand of it
This is the everyday Greek word for hair. It covers a whole head of hair and a single strand alike, and it names the hair of people and animals without any change in meaning: the same word describes the woman's hair that dried Jesus' feet, the camel's hair of John the Baptist's clothing, and the woman-like hair of the locusts in Revelation.
Several of its most memorable appearances are fixed sayings that use a hair as a picture of the smallest, most countable thing. "The very hairs of your head are all numbered" makes God's care exact and personal; "not a hair of your head will perish" promises complete safety. The word itself stays plain; the weight is carried by the saying, not by any special sense of the word.
A close relative is κόμη, which names hair as a styled, flowing head of hair worn as an adornment. By contrast this word points at hair as a physical substance or at an individual strand, which is why it, and not the other, is the word for animal hair and for counting single hairs.