White-Knuckle Meaning

(idiomatic) Causing fear, excitement, apprehension, suspense, or nervousness.

Example: 2010 July 16, Colleen Long and Harry R. Weber, "BP capped well holding nearly a day into new fix", Associated Press wire:
  BP said its capped-off well appeared to be holding steady Friday morning, almost midway into a white-knuckle waiting period in which engineers watched the pressure gauges for signs of a leak.
2009 November 27, “Jimi Hendrix's Voodoo Child has 'best guitar riff'”[1], BBC:
  "No surprise given both Bellamy and White share - or have inherited - Hendrix's unique blend of experimental instincts and white-knuckle showmanship," said Mr Goldsmith.