nerveless

adjectives

marked by calm self-control (especially in trying circumstances); unemotional
"play it cool"; "keep cool"; "stayed coolheaded in the crisis"; "the most nerveless winner in the history of the tournament"
cool, coolheaded, nerveless
is derived from
nervelessness
lacking strength
"a weak, nerveless fool, devoid of energy and promptitude"- Nathaniel Hawthorne
feeble, nerveless