very thin, as thin as a hair
A fishing line made from hair.
The line along one's forehead where hair starts growing.
A very thin line in writing, drawing, or typography.
A very thin fissure.
Very small.
Incalculably, exceedingly, or immeasurably minute; vanishingly small.
Of or pertaining to values that approach zero as a limit.
A non-zero quantity whose magnitude is smaller than any positive number (by definition it is not a real number).