rotation-inversion axis

[ roh-tey-shuh n in-vur-zhuh n, -shuh n ]
/ roʊˈteɪ ʃən ɪnˈvɜr ʒən, -ʃən /

noun Crystallography.

an axis of a crystal such that rotating about the axis and then inverting the crystal brings the crystal back to its original position.
Also called symmetry axis of rotary inversion.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019