Whiteknucklers is a term that refers to experiences or situations that are extremely tense, nerve-wracking, or frightening. When searching for synonyms for this term, some options include nail-biters, heart-stoppers, thrill rides, nerve-janglers, edge-of-your-seat moments, and adrenaline rushes. All of these expressions convey a sense of high intensity, drama, and excitement, and can be used to describe a range of experiences from watching a thrilling movie to going on a rollercoaster ride. While the origin of the term "whiteknucklers" is unclear, what is clear is that it has become a widely recognized expression that captures the feeling of intense fear or excitement.