umbra-, umbro-, umbr-, umbel-

(Latin: shade, shadow)

abumbral (adjective) (not comparable)
Relating to the top surface of a jellyfish; exumbrellar: Mary learned that a large siphonophore, for example a man-of-war, had an abumbral outer covering that looked like an umbrella.
adumbral (adjective), more adumbral, most adumbral
Descriptive of a shadowy or shady condition.
adumbrant (adjective), more adumbrant, most adumbrant
A reference to giving a faint shadow or a slight resemblance to something that might happen.
adumbrate (verb), adumbrates; adumbrated; adumbrating
1. To give an incomplete or faint outline or indication of something.
2. To give a vague indication or warning of something to come.
3. To overshadow and obscure something.
4. To give a faint shadow, or slight likeness; to exhibit a faint resemblance, like a shadow.
adumbration (s) (noun), adumbrations (pl)
1. The act of making a shadow or faint resemblance.
2. The shadowing or partial concealment of an area.
3. A faint sketch; an imperfect representation of a thing.
4. In heraldry, the shadow only of a figure, outlined, and painted of a color darker than the field.
adumbrative (adjective), more adumbrative, most adumbrative
Faintly indicating something.
adumbratively (sdverb), more adumbratively, most adumbratively
Conveying a suggestion, a declaration, a partial outline of, or the foreshadowing of something.
1. With some structure overhanging the parts so as partially to conceal them.
2. To shade; to darken; to cloud.
penumbra (s) (noun), penumbrae (pl)
1. In astronomy, a partial outer shadow that is lighter than the darker inner shadow ("umbra"): Penumbra is the area between complete darkness and the complete light in an eclipse.
2. An indistinct area; especially, a situation in which something is unclear or uncertain: In astronomy, a penumbra is a grayish area surrounding the dark center of a sunspot.
3. The outer region or periphery of something: A penumbra area is covered by shadiness, so it is not completely dark.
4. Etymology: from Modern Latin penumbra. "partial shadow outside the complete shadow of an eclipse"; coined in 1604 by Kepler from Latin pæne, "almost" + umbra, "shadow".
Pulvis et umbra (sumus).
We are but dust and shadow.
somber, sombre (British), sombrous
1. Lacking light or brightness and producing a dull, dark, or melancholy atmosphere.
2. Having a color or tone that is dark, dull, or suitable for a serious mood or occasion.
3. Marked by or conveying strict seriousness combined with sadness or a troubled state of mind.

Via French, "gloomy", ultimately from late Latin subumbrare, “to shadow" from sub, "under" plus umbra, "shade"; the source of English umbrage.

In a somber manner: that is, with a gloomy, depressing, or dismal attitude.
A straw or felt hat with a very wide upturned brim, originally worn by men in Mexico and some other Spanish-speaking countries.

Via Spanish, "hat", from sombra "shade"; previously from Vulgar Latin sumombrare.

The concave oral surface of the umbrella of a medusa (jelly fish); the concave inner surface of the medusoid bell.
umbel, umbellate, umbella
1. In botany [diminutive of umbra, shadow], a flat-topped or rounded flower cluster (umbrella-shaped flower head) in which the individual flower stalks spring from about the same point in an axis, as in the carrot, parsley, dill, fennel, and related plants.
2. A typically umbrella-shaped inflorescence in which all pedicels arise at the apex of an axis; commonly compound.

Other related "dark; shadow, shade; black" units: lygo-; melan-; nigri-; nocti-; nycti-; scoto-; skio-.