hair/ hεər /

1.noun [u] 
(human) (on head) 头发

2.noun [u] 
(on body) 汗毛

3.noun [c] 
(single strand) 毛发

4.noun [c/u] 
(animal on body,single strand) 毛毛

5.noun [c] 
(on plants and insects) 绒毛

to do one's hair
梳头
to have {or} get one's hair done
打理头发
to have {or} get one's hair cut
剪头发
by a hair's breadth
 [fig] 极端的距离
to let one's hair down
 [fig] 放松一点
to make sb's hair stand on end
 [fig] 使某人毛骨悚然
not a hair out of place
衣着一丝不乱
he didn't turn a hair
泰然处之
to get in sb's hair
惹恼某人