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.
Fitful or unsteady.
Not certain; unsure.
Not yet determined; undecided.
Variable and subject to change.
Unpredictable or capricious.
Not known for certain; questionable.
Something uncertain.