hair has 7 distinct synonyms spread across 4 of its 6 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a covering for the body (or parts of it) consisting of a dense growth of threadlike structures (as on the human head); helps to prevent heat loss
“he combed his hair”
Synonyms, antonyms and the broader and narrower relations for hair come from Princeton University’s WordNet. Full sources and licences.
a very small distance or space
“they escaped by a hair's-breadth”
filamentous hairlike growth on a plant
“peach fuzz”
any of the cylindrical filaments characteristically growing from the epidermis of a mammal
“there is a hair in my soup”