The Collaborative International Dictionary of English v.0.48:
Rhomb \Rhomb\ (r[o^]mb or r[o^]m; 277), n. [L. rhombus, Gr.
"ro`mbos rhomb, a spinning top, magic wheel, fr. "re`mbein to
turn or whirl round, perhaps akin to E. wrench: cf. F.
rhombe. Cf. Rhombus, Rhumb.]
1. (Geom.) An equilateral parallelogram, or quadrilateral
figure whose sides are equal and the opposite sides
parallel. The angles may be unequal, two being obtuse and
two acute, as in the cut, or the angles may be equal, in
which case it is usually called a square.
2. (Geom.) A rhombohedron.
Fresnel's rhomb (Opt.), a rhomb or oblique parallelopiped
of crown or St. Gobain glass so cut that a ray of light
entering one of its faces at right angles shall emerge at
right angles at the opposite face, after undergoing within
the rhomb, at other faces, two reflections. It is used to
produce a ray circularly polarized from a plane-polarized
ray, or the reverse. --Nichol.