out of a clear blue sky

noun, plural skies. Often skies (for defs 1–4).

1. the region of the clouds or the upper air; the upper atmosphere of the earth: airplanes in the sky; cloudy skies.
2. the heavens or firmament, appearing as a great arch or vault.
3. the supernal or celestial heaven: They looked to the sky for help.
4. the climate: the sunny skies of Italy.
5. Obsolete. a cloud.

verb (used with object), skied or skyed, sky·ing.

6. Informal. to raise, throw, or hit aloft or into the air.
7. Informal. to hang (a painting) high on a wall, above the line of vision.

Verb Phrases

8. sky up, Falconry. (of prey, when flushed) to fly straight upward.

Idioms

9. out of a/the clear sky, without advance notice or warning; abruptly: An old beau phoned her out of a clear sky.Also out of a/the clear blue sky.
10. to the skies, with lavishness or enthusiasm; extravagantly: to praise someone to the skies.Also to the sky.

noun plural skies

1. (sometimes plural) the apparently dome-shaped expanse extending upwards from the horizon that is characteristically blue or grey during the day, red in the evening, and black at nightRelated adjectives: celestial, empyrean
2. outer space, as seen from the earth
3. (often plural) weather, as described by the appearance of the upper airsunny skies
4. the source of divine power; heaven
5. informal the highest level of attainmentthe sky’s the limit
6. to the skies highly; extravagantly

verb skies, skying or skied

7. rowing to lift (the blade of an oar) too high before a stroke
8. (tr) informal to hit (a ball) high in the air

n.c.1200, “a cloud,” from Old Norse sky “cloud,” from Proto-Germanic *skeujam “cloud, cloud cover” (cf. Old English sceo, Old Saxon scio “cloud, region of the clouds, sky;” Old High German scuwo, Old English scua, Old Norse skuggi “shadow;” Gothic skuggwa “mirror”), from PIE root *(s)keu- “to cover, conceal” (see hide (n.1)). Meaning “upper regions of the air” is attested from c.1300; replaced native heofon in this sense (see heaven). In Middle English, the word can still mean both “cloud” and “heaven,” as still in the skies, originally “the clouds.” Sky-high is from 1812; phrase the sky’s the limit is attested from 1908. Sky-dive first recorded 1965; sky-writing is from 1922. v.“to raise or throw toward the skies,” 1802, from sky (n.).

1. The atmosphere, as seen from a given point on the Earth’s surface. The sky appears to be blue because the wavelengths associated with blue light are scattered more easily than those that are associated with the other colors.

Also, out of the blue. Without warning, suddenly, as in Her offer to help us with the fundraising came out of a clear blue sky, or We got a check from Aunt Ruby out of the blue. These metaphoric terms allude to something dropping unexpectedly from the sky. [Late 1800s] Also see out of nowhere. In addition to the idiom beginning with sky , also see

blow sky-high

out of a clear blue sky

pie in the sky

reach for the sky.