umbral

American  

[uhm-bruhl] / ˈʌm brəl /

adjective

1. of or like a shadow or shadowy apparition.

   Smoke was rising and beginning to coat the clouds a deep, umbral black.

   In an instant the vampire’s corporeal form dematerialized into an umbral form that quickly merged with the surrounding cover of night.

2. Astronomy.

   1. relating to or being the complete shadow of an opaque body, such as a planet, where all direct light from the source of illumination is cut off.

      It was to be a very deep eclipse, with the moon passing very close to the center of Earth's umbral shadow.

   2. relating to or being the dark central portion of a sunspot.

      Umbral flashes—powerful brightenings that shock the darkest part of the sunspot—appear continuously every 2 to 3 minutes.

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Etymology

Origin of umbral

umbra ( def. ) + -al ¹ ( def. )

Example Sentences

In math, Ono is known for his work on a range of topics across number theory, from Ramanujan’s congruences to the umbral moonshine conjecture.

From The Wall Street Journal • Dec. 4, 2025

Over the following hour, the moon advances into the umbral shadow.

From Washington Post • Aug. 29, 2015

The first partial eclipse phase starts at 1:58 a.m., when the moon enters Earth’s umbral shadow.

From Washington Post • Mar. 29, 2014

Yet the person I read about in my recovery diary is childlike and prosaic, unlike that umbral pre-hospital self who could, even at her most obscured, be eerily illuminating.

From The Guardian • Jan. 13, 2013

Outside the umbral cone is that of the penumbra, within which the sun is partially hidden by the moon.

From Encyclopaedia Britannica, 11th Edition, Volume 8, Slice 10 "Echinoderma" to "Edward" by Various

Related Words

• dark
• ghostly
• shady