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.