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 string theory underlying umbral moonshine is likely to be “not just any physical theory, but a particularly important one,” Cheng said.

From Scientific American • Apr. 7, 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

Within the umbral curve the eclipse is annular or total; outside of it and within the penumbral curve the eclipse is partial at the given moment.

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

Related Words

• dark
• ghostly
• shady