umbral

Umbral is an adjective derived from the Latin umbra, meaning shadow. In English it describes something relating to a shadow or darkness, or pertaining to shaded regions produced by blocking light. The term is used across scientific and literary contexts to convey a sense of gloom or concealment as well as physical shadow.

In astronomy, umbra denotes the darkest, fully shaded part of a shadow cone. It is distinct from the penumbra, the lighter outer region where light is only partially blocked. For eclipses, this distinction matters: during a solar eclipse the Moon’s umbra may reach parts of the Earth, producing totality for observers within that cone; observers outside the umbra but inside the penumbra see a partial eclipse. Conversely, during a lunar eclipse the Earth’s umbra falls on the Moon; a total lunar eclipse occurs when the Moon passes completely through the Earth's umbra, while a penumbral eclipse involves only the penumbral shadow.

Beyond science, umbral is used metaphorically to describe things that are shadowy, concealed, or obscure—such as a setting or atmosphere with a somber or mysterious tone, or a scene described as “umbral.” The word also appears in various disciplines when conveying a sense of shade or partial light, including art, architecture, and literature.

Etymology and usage notes: umbral comes from Latin umbra, meaning shade or shadow, and entered English with senses related to darkness and shading. It is often contrasted with penumbra, the lighter, partially shaded region.