Imperceptibility :: Imperceptibility (n.) The state or quality of being imperceptible.
Imperceptible :: Imperceptible (a.) Not perceptible; not to be apprehended or cognized by the souses; not discernible by the mind; not easily apprehended.
Perceptibility :: Perceptibility (n.) The quality or state of being perceptible; as, the perceptibility of light or color..