Aplomb \A`plomb"\, n. [F., lit. perpendicularity; ? to + plomb lead. See {Plumb}.] Assurance of manner or of action; self-possession. web1913

aplomb n : great coolness and composure under strain; "keep your cool" [syn: {assuredness}, {cool}, {poise}, {sang-froid}, {self-possession}] wn