hair·line 
/ˈheɚˌlaɪn/ noun
plural hair·lines /ˈheɚˌlaɪn/ noun [count] 1 : a thin line or crack
▪ The plate had a hairline running across it. — often used before another noun ▪ a hairline crack ▪ He suffered a hairline fracture of his shin bone. 2 : the line where your hair starts on your forehead
▪ He has a receding hairline.
▪ The plate had a hairline running across it. — often used before another noun ▪ a hairline crack ▪ He suffered a hairline fracture of his shin bone.
▪ He has a receding hairline.
