Definition of white-knuckler in US English:

white-knuckler

noun

North American
informal
  • 1An event or experience provoking extreme fear, suspense, or anxiety; a very frightening or suspenseful book, film, etc.

  • 2A person with an extreme fear of something (especially flying); a tense or anxious person.

Origin

1960s; earliest use found in The Wisconsin State Journal.