hang (on) by a hair

hang (on) by a hair

1. Literally, to be attached only by something very thin and precarious. If that button is only hanging by a thread, you're bound to lose it during the course of the day.
2. To be perilously close to failing, dying, or resulting in a bad outcome. After the loss, their chances of getting into the championships are hanging on by a thread. Her life hung by a thread as medics rushed her to the hospital.
See also: by, hair, hang
Farlex Dictionary of Idioms.

hang by a hair

 and hang by a thread 
1. Lit. to hang by something very thin, such as a thread or a hair. The tiniest part of the mobile hung by a thread, the rest are on plastic cords.
2. and hang on by a hair; hang on by a thread Fig. to depend on something very insubstantial; to hang in the balance. Your whole argument is hanging by a thread. John isn't failing geometry, but his passing grade is just hanging by a hair.
See also: by, hair, hang
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • hang by a hair
  • hang by a thread
  • hang by a thread, to
  • hang by a thread/hair
  • eye of the needle
  • the eye of a needle
  • thread the needle
  • right on the button
  • ride a tiger
  • at the touch of a button