hairline
UK: ˈheəlaɪn | US: ˈherlaɪn
n. the edge of a person's hair, especially where it meets the forehead
n. a very thin line or crack, often barely visible
adj. describing something extremely fine or precise (e.g., a hairline fracture)
The word "hairline" combines "hair," derived from Old English hǣr (related to Germanic hēr), and "line," from Latin linea (via Old French ligne). It originally described the natural boundary of hair on the scalp, later extended metaphorically to denote anything extremely fine or narrowly defined, like a thin crack or precise measurement. The logic reflects a visual analogy—the delicacy of a single hair strand as a marker of subtlety.
His receding hairline became more noticeable with age.
The vase had a hairline crack that was almost invisible.
Surgeons made a hairline incision to minimize scarring.
The artist drew a hairline border around the portrait.
Detectives found a hairline fracture in the glass, suggesting forced entry.