mirror image

WordReference Random House Unabridged Dictionary of American English © 2025

mir′ror im′age, 

1. an image of an object, plan, person, etc., as it would appear if viewed in a mirror, with right and left reversed.
2. an object having a spatial arrangement that corresponds to that of another object except that the right-to-left sense on one object corresponds to the left-to-right sense on the other.
• 1880–85

Collins Concise English Dictionary © HarperCollins Publishers::

mirror image noun

1. an image as observed in a mirror
2. an object that corresponds to another object in the same way as it would correspond to its image in a mirror