1791, "action or process of reconstructing," noun of action to go with reconstruct. In U.S. history, usually with a capital R-, it has been used from 1865 in reference to the process (lasting until about 1870) by which the states which had seceded were restored to the rights and privileges of the Union. It had been used in the U.S. during the American Civil War in reference to the anticipated reconstitution of the Union. Hence, for a time, in American English, reconstructed "altered by Reconstruction" (1865).
"form again, remake, reconstruct, re-create or re-establish," mid-14c., from re- "back, again" + form (v.). Intransitive sense of "form again, get into order or line again" also is from mid-14c. Spelled with a hyphen from 17c. to distinguish it from the specific sense in reform; this is the original meaning of that word, still in use but now with full pronunciation of the prefix. Related: Re-formed; re-forming; re-formation.
late 14c., reformen, "to convert into or restore to another and better form" (of strength, health, firmness, etc.), from Old French reformer "rebuild, reconstruct, recreate" (12c.) and directly from Latin reformare "to form again, change, transform, alter," from re- "again" (see re-) + formare "to form" (see form (n.)).
The meaning "change (someone or something) for the better, correct, improve; bring (someone) away from an evil course of life" is recorded from late 14c.; of governments, institutions, etc., from early 15c. Intransitive sense of "abandon wrongdoing or error" is by 1580s. Related: Reformed; reforming. Reformed churches (1580s) on the European continent were usually Calvinist as opposed to Lutheran (in France they were the Huguenots). Reformed Judaism (1843) is a movement initiated in Germany by Moses Mendelssohn (1729-1786). Reform school is attested from 1859.
season after summer and before winter, late 14c., autumpne (modern form from 16c.), from Old French autumpne, automne (13c.), from Latin autumnus (also auctumnus, perhaps influenced by auctus "increase"), which is of unknown origin. Perhaps from Etruscan, but Tucker suggests a meaning "drying-up season" and a root in *auq- (which would suggest the form in -c- was the original) and compares archaic English sere-month "August." De Vaan writes, "Although 'summer', 'winter' and 'spring' are inherited IE words in Latin, a foreign origin of autumnus is conceivable, since we cannot reconstruct a PIE word for 'autumn'".
Harvest (n.) was the English name for the season until autumn began to displace it 16c. Astronomically, from the descending equinox to the winter solstice; in Britain, the season is popularly August through October; in U.S., September through November. Compare Italian autunno, Spanish otoño, Portuguese outono, all from the Latin word.
As de Vaan notes, autumn's names across the Indo-European languages leave no evidence that there ever was a common word for it. Many "autumn" words mean "end, end of summer," or "harvest." Compare Greek phthinoporon "waning of summer;" Lithuanian ruduo "autumn," from rudas "reddish," in reference to leaves; Old Irish fogamar, literally "under-winter."