(ˈ)rō|shōⁿ- noun
Usage: usually capitalized R
Etymology: after Alexis M. Rochon died 1817 French astronomer and optician
: a polarizing prism consisting of two equal prisms of calcite or other doubly refracting material cut so that the optic axis of one of the prisms is parallel to its refracting edge, the axis of the other is perpendicular to its refracting edge, and the directions of the optic axes make angles of 90 degrees with each other