[hair.line] n (1846) 1: a very slender line: as a: a tiny line or crack on a surface "a ~ bone fracture" b: a fine line connecting thicker strokes in a printed letter
2: hairbreadth 3 a: a textile design consisting of lengthwise or crosswise lines usu. one thread wide b: a fabric with such a design
4. a: the outline of scalp hair esp. on the forehead b: the way the hair frames the face -- hairline adj