hairline

noun4

1. •
   The line along one's forehead where hair starts growing.

   • It's just a receding hairline — it's not like you're going bald.
2. •
   (figurative) A very thin fissure.

   • While inspecting the new house, we found a few hairlines in one of the walls.
   • There was a hairline crack in the airplane's wing.
3. •
   A very thin line in writing, drawing, or typography.
4. •
   A fishing line made from hair.