Synonyms for Nerveless (same or very similar meaning)
WordNet sense 1 (lacking strength):
feeble
WordNet sense 2 (lacking power):
powerless
WordNet sense 3 (marked by calm self-control (especially in trying circumstances); unemotional):
cool, coolheaded
WordNet sense 4 (serenely self-possessed and free from agitation especially in times of stress):
composed
From the ODE community, based on WordNet
add/edit