Old English ofersceadwian "to cast a shadow over, obscure;" see over + shadow (v.). It was used to render Latin obumbrare in New Testament, as were Middle High German überschatewen, Middle Dutch overschaduwen, Gothic ufarskadwjan in those languages. Figurative sense is from 1580s. Related: Overshadowed; overshadowing.
Proto-Indo-European root meaning "dark, shade."
It is the hypothetical source of/evidence for its existence is provided by: Greek skotos "darkness, gloom;" Albanian kot "darkness;" Old Irish scath, Old Welsh scod, Breton squeut "darkness," Gaelic sgath "shade, shadow, shelter;" Old English scead "partial darkness," sceadu "shade, shadow, darkness," Dutch schaduw, German Schatten, Gothic skadus "shadow."
1660s, "partially shaded region around the shadow of an opaque body, a partial shadow," from Modern Latin penumbra "partial shadow outside the complete shadow of an eclipse," coined 1604 by Kepler from Latin pæne "nearly, almost, practically," which is of uncertain origin, + umbra "shadow" (see umbrage). Figurative use is by 1801. Related: Penumbral.
All points within the penumbra are excluded from the view of some part of the luminous body, and are thus partially shaded; while all points within the umbra, or total shadow, are completely excluded from view of the luminous body. [Century Dictionary]
1550s, "faint sketch, imperfect representation," from Latin adumbrationem (nominative adumbratio) "a sketch in shadow, sketch, outline," noun of action from past-participle stem of adumbrare "to cast a shadow, overshadow," in painting, "represent (a thing) in outline," from ad- "to" (see ad-) + umbrare "to cast in shadow," from PIE root *andho- "blind; dark" (see umbrage).
1760 "gloomy, shadowy" (earlier sombrous, c. 1730), from French sombre "dark, gloomy," from Old French sombre (14c.), from an adjective from Late Latin subumbrare "to shadow," from sub "under" (see sub-) + umbra "shade, shadow" (perhaps from a suffixed form of PIE *andho- "blind, dark;" see umbrage). Related: Somberly; somberness.