A nerve-racking situation pulls your nerves tight: you feel very worried, jumpy, or on edge while it is happening. Waiting for exam results, speaking in front of the class, sitting in the dentist’s chair, watching a match in the last minute — those can all be nerve-racking. The word usually describes the thing or the time, not the person. You feel nervous; the wait is nerve-racking. You will also see nerve-wracking, with a w. Though actually both spellings are in wide use, and teachers argue about them. The older idea is racking: to rack something is to stretch it hard, like the old torture frame called a rack, so your nerves are being pulled. Wrack is an old word for wreck and ruin, so nerve-wracking paints a slightly different picture. In real life, people do not choose the spelling by meaning; they write the one they have seen. Either will be understood. It is everyday English, fine in speech and in newspapers, a little heavy for the most careful formal writing, where someone might say “very stressful” instead.