somber adj.

word-forming element meaning "under, beneath; behind; from under; resulting from further division," from Latin preposition sub "under, below, beneath, at the foot of," also "close to, up to, towards;" of time, "within, during;" figuratively "subject to, in the power of;" also "a little, somewhat" (as in sub-horridus "somewhat rough"), from PIE *(s)up- (perhaps representing *ex-upo-), a variant form of the root *upo "under," also "up from under." The Latin word also was used as a prefix and in various combinations.

In Latin assimilated to following -c-, -f-, -g-, -p-, and often -r- and -m-. In Old French the prefix appears in the full Latin form only "in learned adoptions of old Latin compounds" [OED], and in popular use it was represented by sous-, sou-; as in French souvenir from Latin subvenire, souscrire (Old French souzescrire) from subscribere, etc.

The original meaning is now obscured in many words from Latin (suggest, suspect, subject, etc.). The prefix is active in Modern English, sometimes meaning "subordinate" (as in subcontractor); "inferior" (17c., as in subhuman); "smaller" (18c.); "a part or division of" (c. 1800, as in subcontinent).

early 15c., "shadow, darkness, shade," from Old French ombrage "shade, shadow," from noun use of Latin umbraticum "of or pertaining to shade; being in retirement," neuter of umbraticus "of or pertaining to shade," from umbra "shade, shadow," from PIE root *andho- "blind; dark" (source also of Sanskrit andha-, Avestan anda- "blind, dark").

The English word had many figurative uses in 17c.; the one remaining, "suspicion that one has been slighted," is recorded by 1610s; hence phrase to take umbrage at, attested from 1670s. Perhaps the sense notion is similar to whatever inspired the modern (by 2013) slang verbal phrase throw shade "(subtly) insult (something or someone)."