(plural scotomata), 1875 as "defect in the visual field," from Late Latin scotoma, from Latinized form of Greek skotōma "dizziness," from skotoun "to darken," from skotos "darkness" (from PIE root *skoto- "dark, shade."). Earlier as "dizziness accompanied by dimness of sight" (1540s). Related: Scotomatical.
late 14c., "to remove the dimness or blindness" (usually figurative, from one's eyes or heart); see en- (1) + lighten (v.2). From 1660s as "supply with intellectual light." Literal senses are later and less common in English: "put light in" is from 1580s; "shed light upon" is from 1610s. Related: Enlightened; enlightening. Old English had inlihtan "to illuminate, enlighten."
Old English dimm "dark, gloomy, obscure; not clearly seen, indistinct," from Proto-Germanic *dimbaz (source also of Old Norse dimmr, Old Frisian dim, Old High German timber "dark, black, somber"). Not known outside Germanic.
Of eyes, "not seeing clearly," early 13c. Of sound from early 14c.; of light, "not bright, faintly luminous," from early 14c. Modern slang sense of "dull of apprehension, stupid" is from 1892; the sense of "dull-witted" also was in Middle English (mid-13c.). Related: Dimly; dimness.
"weather condition consisting of a cloud resting upon the ground, fog," also "precipitation consisting of fine droplets of water, much smaller than rain," Old English mist (earliest in compounds, such as misthleoðu "misty cliffs," wælmist "mist of death"), from Proto-Germanic *mikhstaz (source also of Middle Low German mist, Dutch mist, Icelandic mistur, Norwegian and Swedish mist), perhaps from PIE *meigh- "to urinate." Greek omikhle "fog;" Old Church Slavonic migla"fog;" Sanskrit mih- "fog, mist," megha "cloud" sometimes are said to be cognates in this secondary sense, but Beekes finds these rather more likely to be from a separate IE root meaning "fog."
Sometimes distinguished from fog, either as being less opaque or as consisting of drops large enough to have a perceptible downward motion. [OED]
Also in Old English in reference to dimness of the eyes or eyesight, either by illness or tears, and in a figurative sense of "something that darkens and obscures mental vision." Meaning "haze of dust in the air producing obscurity of things seen at a distance" is by 1785.