Rhomb (?), n. [L. rhombus, Gr.
??? rhomb, a spinning top, magic wheel, fr. ??? 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.