Adjective. If your hands are white-knuckled, you are holding on so tightly that the skin over your knuckles (the bones at the base of your fingers) goes pale — the blood is squeezed out of it. So the word is a picture of fear or great tension, not really a description of colour. You see it in phrases like "white-knuckled hands", "a white-knuckled grip on the steering wheel", "white-knuckled passengers". Though actually, the word has drifted. Very often it no longer describes the hands at all — it describes the whole experience: "a white-knuckle ride", "a white-knuckle finish", "three white-knuckle hours in the storm". Here it means terrifying and exciting at once, and this is now the more common use, especially in newspapers and in advertisements for theme parks. Note the form: for the experience, people usually drop the -d and say white-knuckle; for the person or the hands, they usually keep it — white-knuckled. Both are informal-to-neutral, never formal writing. There is a third, quieter use: to be white-knuckling something means to get through it by pure force of will, holding on when you want to let go — "he white-knuckled his way through the speech". This one is common in American English and in recovery talk ("white-knuckle sobriety" = staying off alcohol by gritted teeth alone, with no real peace about it).

（手）因緊張害怕而握得死緊、指節發白；引申指「驚險刺激的」（如 white-knuckle ride 驚險刺激的遊樂設施）