When a given substance has a different absorbance for the right polarized light in comparison to the left one at a particular wavelength we say that a circular dichroism effect is observed at that wavelength. In fact, circular dichroism is the absorption difference between left and right circularly polarized light at a given wavelength.
Note that dichroism is a word derived from Ancient Greek which means "two-colors", because the sample under analysis has one color if illuminated with the right polarized light and a different color if illuminated with the left one. The color, in fact, depends on light absorption.

What happens to our magenta electric-field vector when circular dichroism occurs ?
As we have already said, the two circular polarized components are differently absorbed, so that the corresponding intensities are different.
If we apply again the vector decomposition rules at different times, we see that the magenta resulting vector is no more confined to the original plane of polarization.
On the contrary, it starts to describe an elliptic trajectory (in the illustrated case, anticlockwise).

The ratio of the minor to the major axis of the ellipse is by definition the tangent of the angle teta (blue). This angle is called ellipticity, while the angle OR is called optical rotation.
As we saw, the ellipticity is a direct consequence of the presence of circular dichroism. More importantly, it can be shown that the ellipticity is directly proportional to the circular dichroism, and in particular that:

q = 32.98 CD

To remove the dependence on cuvette path length and solute concentration, one can use molar ellipticity, defined as:

[q] = 100 q / C l

where C is the solute molarity and l the cuvette path length. The factor 100 is due to the use of measure this last quantity in cm.
The dimensions of molar ellipticity are thus:

100 deg dm³ mol^-1 cm^-1 = 100 deg cm³/1000 mol^-1 cm^-1 = deg cm²/10 mol^-1 =

deg cm² dmol^-1