nail biter

noun2

1. •
   One who habitually bites or chews their fingernails.

   • But Victor did not reveal any behavior disorder, did not pick his nose, did not suck his thumb, was not even a nail biter. — 1957
2. •
   (figurative) A situation which causes anxiety, suspense, nervousness or discomfort.

   • It was a real nail biter waiting for the test results.