imperturbable

cool, composed, collected, unruffled, imperturbable, nonchalant mean free from agitation or excitement. cool may imply calmness, deliberateness, or dispassionateness <kept a cool head>. composed implies freedom from agitation as a result of self-discipline or a sedate disposition <the composed pianist gave a flawless concert>. collected implies a concentration of mind that eliminates distractions especially in moments of crisis <the nurse stayed calm and collected>. unruffled suggests apparent serenity and poise in the face of setbacks or in the midst of excitement <harried but unruffled>. imperturbable implies coolness or assurance even under severe provocation <the speaker remained imperturbable despite the heckling>. nonchalant stresses an easy coolness of manner or casualness that suggests indifference or unconcern <a nonchalant driver>.