windfall (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.

Old English feallan (class VII strong verb; past tense feoll, past participle feallen) "to drop from a height; fail, decay, die," from Proto-Germanic *fallanan (source also of Old Frisian falla, Old Saxon fallan, Dutch vallen, Old Norse falla, Old High German fallan, German fallen, absent in Gothic).

These are from PIE root *pol- "to fall" (source also of Armenian p'ul "downfall," Lithuanian puolu, pulti "to fall," Old Prussian aupallai "finds," literally "falls upon").

The meaning "come suddenly to the ground" is from late Old English. Of darkness, night, from c. 1600; of land sloping from 1570s; of prices from 1570s. Of empires, governments, etc., from c. 1200. Of the face or countenance from late 14c. The meaning "to be reduced" (as temperature) is from 1650s. That of "die in battle" is from 1570s. The meaning "to pass casually (into some condition)" is from early 13c.

To fall in "take place or position" is from 1751. To fall in love is attested from 1520s; to fall asleep is late 14c. (Middle English also used slide asleep, etc.). To fall down is early 13c. (a-dun follon); to fall behind is from 1856. Fall through "fail, come to nothing" is from 1781. To fall for something is from 1903.

To fall out is by mid-13c. in a literal sense; military use is from 1832. The meaning "have a disagreement, begin to quarrel" is attested from 1560s (to fall out with "quarrel with" is from late 15c.).