windmill n.

"air in motion," Old English wind "wind," from Proto-Germanic *winda- (source also of Old Saxon, Old Frisian, Middle Dutch, Dutch wind, Old Norse vindr, Old High German wind, German Wind, Gothic winds), from PIE *wē-nt-o‑ "blowing," suffixed (participial) form of root *we- "to blow."

Normal pronunciation evolution made this word rhyme with kind and rind (Donne rhymes it with mind and Thomas Moore with behind), but it shifted to a short vowel 18c., probably from influence of windy, where the short vowel is natural. A sad loss for poets, who now must rhyme it only with sinned and a handful of weak words. Symbolic of emptiness and vanity since late 13c.

I have forgot much, Cynara! gone with the wind. [Ernest Dowson, 1896]

Meaning "breath" is attested from late Old English; especially "breath in speaking" (early 14c.), so long-winded, also "easy or regular breathing" (early 14c.), hence second wind in the figurative sense (by 1830), an image from the sport of hunting.

Winds "wind instruments of an orchestra" is from 1876. Figurative phrase which way the wind blows for "the current state of affairs" is suggested from c. 1400. To get wind of "receive information about" is by 1809, perhaps inspired by French avoir le vent de. To take the wind out of (one's) sails in the figurative sense (by 1883) is an image from sailing, where a ship without wind can make no progress. Wind-chill index is recorded from 1939. Wind energy from 1976. Wind vane from 1725.

Middle English mille, "building fitted to grind grain," Old English mylen "a mill" (10c.), an early Germanic borrowing from Late Latin molina, molinum "mill" (source of French moulin, Spanish molino), originally fem. and neuter of molinus "pertaining to a mill," from Latin mola "mill, millstone," related to molere "to grind," from PIE root *mele- "to crush, grind." The -n- gradually was lost in English but survives in the surname Milner. Also from Late Latin molina, directly or indirectly, are German Mühle, Old Saxon mulin, Old Norse mylna, Danish mølle, Old Church Slavonic mulinu.

The meaning "mechanical device for grinding grain for food" is from 1550s. The broader sense of "machine for grinding or pulverizing any solid substance" is attested from 1670s. Other types of manufacturing machines driven by wind or water, that transform raw material by a process other than grinding began to be called mills by early 15c. Sense of "large building fitted with machinery for manufacturing" is from c. 1500. In old slang also "a typewriter" (1913); "a boxing match or other pugilistic bout" (1819).