In the sense you are meeting here, nerveless describes someone’s fingers (or sometimes hands) when they cannot hold a thing firmly. After a shock — bad news, a near miss, a sudden fright — the hands can go slack, as if the strength has run out of them. A glass slips. A pen drops. We say the fingers were nerveless. “Nerve” here is not “worry”; it is the living strength and feeling in the body. Take that away, and the grip goes. Though actually this is not the only way English uses the word, and the other way can look like the opposite. In sport, and in stories about brave people, nerveless often means “not nervous at all”: a nerveless penalty kick, someone whose hands do not shake when it matters. Same pieces, two pictures: no strength in the fingers, or no fear in the heart. You tell them apart from the rest of the sentence. The “slack after a shock” meaning is a little more like story-language; the “calm under pressure” meaning is the one you will hear when people talk about sport. There is also an older use, “without courage,” but you can live without that one for now.

手指發軟、握不住（受驚嚇時）；另一常見義是沉著、一點都不緊張