Why is the ninth month called September?
Old English mist "dimness (of eyesight), mist" (earliest in compounds, such as misthleoðu "misty cliffs," wælmist "mist of death"), from Proto-Germanic *mikhstaz (cf. Middle Low German mist, Dutch mist, Icelandic mistur, Norwegian and Swedish mist), perhaps from PIE *meigh- "to urinate" (cf. Greek omikhle, Old Church Slavonic migla, Sanskrit mih, megha "cloud, mist;" see micturition).
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 sense of "dimness of the eyes, either by illness or tears," and in figurative sense of "things that obscure mental vision."
Old English mistian "to become misty, to be or grow misty;" see mist (n.). Meaning "To cover with mist" is early 15c. Related: Misted; misting.
A mass of fine droplets of water in the atmosphere near or in contact with the Earth. Mist reduces visibility to not less than 1 km (0.62 mi). Compare fog.