device to make an air current, Old English fann (West Saxon) "a basket or shovel for winnowing grain" (by tossing it in the air), from Latin vannus, related to ventus "wind" (see wind (n.1)).
The chaff, being lighter, would blow off. Sense of "device for moving air" first recorded late 14c.; the hand-held version is first attested 1550s. A fan-light (1819) was shaped like a lady's fan.
"devotee," 1889, American English, originally of baseball enthusiasts, probably a shortening of fanatic, but may be influenced by the fancy, a collective term for followers of a certain hobby or sport (especially boxing); see fancy. There is an isolated use from 1682, but the modern word is likely a late 19c. formation. Fan club attested by 1930.
late Old English fannian "to winnow grain," from the noun (see fan (n.1)). Meaning "to stir up air" is from early 15c. Related: Fanned; fanning. To fan out "spread out like a hand-held fan," is from 1590s.
To cause or experience extensive trouble and chaos: A month later it all hit the fan/ Meanwhile the mailings had hit the fan
a winnowing shovel by which grain was thrown up against the wind that it might be cleansed from broken straw and chaff (Isa. 30:24; Jer. 15:7; Matt. 3:12). (See AGRICULTURE.)