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principal axis

American  

noun

  1. Optics. a line passing through the center of the surface of a lens or spherical mirror and through the centers of curvature of all segments of the lens or mirror.

  2. Physics. one of three mutually perpendicular axes of a body about which the moment of inertia is maximum or minimum.

principal axis British  

noun

  1. the line passing through the optical centre and centres of curvature of the faces of a lens or a curved mirror

  2. any of three mutually perpendicular axes about which the moment of inertia of a body is maximum

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Etymology

Origin of principal axis

First recorded in 1875–80

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.