noun
- imperturbable self-possession, poise, or assurance.
- the perpendicular, or vertical, position.
noun
- equanimity, self-confidence, or self-possession
“assurance, confidence,” 1828, from French aplomb (16c.), literally “perpendicularity,” from phrase à plomb “poised upright, balanced,” literally “on the plumb line,” from Latin plumbum “(the metal) lead” (see plumb (n.)), of which the weight at the end of the line was made.