fall (v.) - O.E. feallan (class VII strong verb; past tense feoll, pp. feallen), from P.Gmc. *fallanan (cf. O.N. falla, O.H.G. fallan), from PIE base *phol- "to fall" (cf. Armenian p'ul "downfall," Lith. puola "to fall," O.Prus. aupallai "finds," lit. "falls upon"). Noun sense of "autumn" (now only in U.S.) is 1664, short for fall of the leaf (1545). That of "cascade, waterfall" is from 1579. Most of the figurative senses had developed in M.E. Meaning "to be reduced" (as temperature) is from 1658. To fall in love is 1530; to fall asleep is 1393. Fall guy is from 1906. Fallout "radioactive particles" is from 1950. Fallen "morally ruined" is from 1628.

http://www.etymonline.com/f1etym.htm


autumn - c.1380, from O.Fr. autumpne, from L. autumnus, a word probably of Etruscan origin. Harvest was the Eng. name for the season until autumn began to displace it 16c. In Britain, the season is popularly August through October; in U.S., September through November.

http://www.etymonline.com/a7etym.htm