[uncountable, countable] the substance that looks like a mass of fine threads growing especially on the head; one of these threads growing on the body of people and some animals fair/dark hair straight/curly/wavy hair to comb/brush your hair She often wears her hair loose. (informal) I'll be down in a minute. I'm doing (= brushing, arranging, etc.) my hair. I'm having my hair cut this afternoon. He’s losing his hair (= becoming bald). body/facial/pubic hair There's a hair in my soup. The rug was covered with cat hairs.