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Related to principal axis: centre of curvature
1. (General Physics) the line passing through the optical centre and centres of curvature of the faces of a lens or a curved mirror
2. (General Physics) any of three mutually perpendicular axes about which the moment of inertia of a body is maximum
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|Noun||1.||principal axis - a line that passes through the center of curvature of a lens so that light is neither reflected nor refracted; "in a normal eye the optic axis is the direction in which objects are seen most distinctly"|
axis - a straight line through a body or figure that satisfies certain conditions