Old English cludig "rocky, hilly, full of cliffs;" see cloud (n.). Meaning "of the nature of atmospheric clouds" is recorded from c. 1300; meaning "full of clouds, overcast" is late 14c.; of liquids, etc., "not transparent, not clear," from 1580s. Figurative sense of "gloomy" is late 14c. Related: Cloudiness; cloudily.

early 13c., "filled, covered, or sprinkled with dust," from Old English dustig; see dust (n.) + -y (2). As "of the hue of dust; cloudy" from 1670s. Related: Dustiness.

late 14c., "cloudy, misty, hazy" (of the eye, fire-smoke, etc.), from Latin nebulosus "cloudy, misty, foggy, full of vapor," from nebula "mist, vapor" (from PIE root *nebh- "cloud"). The figurative sense of "hazy, vague, formless" is attested by 1831. Astronomical sense, in reference to stars or star clusters surrounded by luminous haze, is from 1670s. Related: Nebulously; nebulousness.

originally the name of the river, from Dakota (Siouan) mnisota, literally "cloudy water, milky water," from mni "river, stream" + sota "slightly clouded." As the name of a U.S. territory from 1849 (admitted as a state 1858). Related: Minnesotan (by 1867).

semi-precious stone, a cloudy white variety of quartz, c. 1300, from Latin calcedonius, a Vulgate rendering of Greek khalkedon in Revelation xxi.19; found nowhere else. "The word is of very complicated history" [OED]. Connection with Chalcedon in Asia Minor "is very doubtful" [OED].

late 14c., "envelop, surround; make cloudy or obscure," from Old French involver and directly from Latin involvere "envelop, surround, overwhelm," literally "roll into," from in- "in" (from PIE root *en "in") + volvere "to roll," from PIE root *wel- (3) "to turn, revolve." Mid-15c. as "concern oneself." Sense of "take in, include" first recorded c. 1600. Related: Involved; Involving.

Obscurest night involved the sky,

The Atlantic billows roared,

[Cowper, "The Castaway"]

early 15c., "closely compacted, thick," from Latin densus "thick, crowded; cloudy," which is of uncertain etymology, perhaps related to Greek dasys "hairy, shaggy; thick with leaves," as a grammatical term, "aspirated," but even this is in doubt. Figurative sense of "difficult to penetrate" (of writing, etc.) is from 1732; that of "stupid" is first recorded 1822. Related: Densely; denseness.