also pre-glacial, "prior to the Ice Ages," 1853, from pre- + glacial.

c. 1300, derken, "to make dark or darker, deprive of light;" early 14c. (intransitive), "to grow or become dark," from dark (adj.) + -en (1). The more usual verb in Middle English in both senses was simply dark, as it is in Chaucer and Shakespeare, and darken did not predominate until 17c. The Anglo-Saxons also had a verb sweorcan meaning "to grow dark."

Meanings "grow less white or clear, turn a darker color" and "render less white or clear" are from late 14c. Figurative sense of "render gloomy, sadden" is from 1742. To darken(one's) door (usually with a negative) "enter one's house as a visitor," usually with an implication of unwelcomeness, is attested from 1729.

surname and masc. proper name, from Irish Donndubhan "dark brown."

1680s, "disposition of light and dark in a picture," literally "bright-dark," from Italian chiaro "clear, bright" (from Latin clarus; see clear (adj.)) + oscuro (from Latin obscurus; see obscure (adj.)). Related: Chiaroscurist.

"to darken, obscure, confuse, bewilder," 1530s, from Latin obfuscatus, past participle of obfuscare "to darken" (usually in a figurative sense), from ob "in front of, before" (see ob-) + fuscare "to make dark," from fuscus "dark" (see dusk). Related: Obfuscated; obfuscating.

Old English deorclice "in a (morally) dark manner, horribly, foully;" see dark + -ly (2). Meaning "mysteriously, with (often sinister) vagueness" is from late 14c.; that of "dimly, obscurely, faintly" is from early 15c.; that of "gloomily, ominously" is from 1590s.

late 13c., "blue, bluish-gray," later "rich, dark blue; purplish-black," from Old French pers "(dark) blue, livid; wan, pale," from Late Latin persus, perhaps a back-formation from one of the early European forms of Persia. Compare indigo, from India.

"with a black or dark appearance," 1560s, from black (adj.) + -ly (2).

"in the dark," mid-15c., from dark (n.) + now-obsolete adverbial ending -ling (compare headlong). The verb darkle is a back-formation from 1810 (Moore, who rhymed it with sparkle), assuming the -ing as a present-participle adjective ending.

But having nothing to do with the participial -ing it does not mean growing dark &c.; from the mistaken notion that it is a participle spring both the misuse of the word itself and the spurious verb darkle. [Fowler]

 By the same error, darkling (adj.), "dark, obscure, gloomy" is attested from 1763. The adverb was sometimes darklings, with adverbial genitive -s.

"greenish-blue color," 1889, short for cyan blue (1879), from Greek kyanos "dark blue, dark blue enamel, lapis lazuli," probably a non-Indo-European word, but perhaps akin to, or from, Hittite *kuwanna(n)- "copper blue."