ETYM Prob. from AS. clűd a rock or hillock, the application arising from the frequent resemblance of clouds to rocks or hillocks in the sky or air.
1. A visible mass of water or ice particles suspended at a considerable altitude.
2. Any collection of particles (e.g., smoke or dust) or gases that is visible.
3. Out of touch with reality.
4. Suspicion affecting one's reputation.
Water vapor condensed into minute water particles that float in masses in the atmosphere. Clouds, like fogs or mists, which occur at lower levels, are formed by the cooling of air containing water vapor, which generally condenses around tiny dust particles.
Clouds are classified according to the height at which they occur and their shape. Cirrus and cirrostratus clouds occur at around 10 km/33,000 ft. The former, sometimes called mares’-tails, consist of minute specks of ice and appear as feathery white wisps, while cirrostratus clouds stretch across the sky as a thin white sheet. Three types of cloud are found at 3–7 km/10,000–23,000 ft: cirrocumulus, altocumulus, and altostratus. Cirrocumulus clouds occur in small or large rounded tufts, sometimes arranged in the pattern called mackerel sky. Altocumulus clouds are similar, but larger, white clouds, also arranged in lines. Altostratus clouds are like heavy cirrostratus clouds and may stretch across the sky as a gray sheet. Stratocumulus clouds are generally lower, occurring at 2–6 km/6,500–20,000 ft. They are dull gray clouds that give rise to a leaden sky that may not yield rain. Two types of clouds, cumulus and cumulonimbus, are placed in a special category because they are produced by daily ascending air cur.
Rents, which take moisture into the cooler regions of the atmosphere. Cumulus clouds have a flat base generally at 1.4 km/4,500 ft where condensation begins, while the upper part is dome-shaped and extends to about 1.8 km/6,000ft. Cumulonimbus clouds have their base at much the same level, but extend much higher, often up to over 6 km/20,000 ft. Short heavy showers and sometimes thunder may accompany them. Stratus clouds, occurring below 1–2.5 km/3,000–8,000 ft, have the appearance of sheets parallel to the horizon and are like high fogs.
In addition to their essential role in the water cycle, clouds are important in the regulation of radiation in the Earth's atmosphere. They reflect short-wave radiation from the Sun, and absorb and re-emit long-wave radiation from the Earth's surface.

1. To billow up in the form of a cloud.
2. To make gloomy or depressed.
3. To make milky or dull.