Hairlines

noun

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. A very thin line in writing, drawing, or typography.
3. A fishing line made from hair.
4. A very thin fissure.

   "While inspecting the new house, we found a few hairlines in one of the walls."