c. 1300, "a gathering of persons, a group gathered for some purpose," from Old French as(s)emblee "assembly, gathering; union, marriage," noun use of fem. past participle of assembler "to assemble" (see assemble). Meaning "a gathering together" is recorded from early 15c.; that of "act of assembling parts or objects" is from 1914, as is assembly line.
Perhaps the most interesting department in the whole factory, to the visitor, is the final assembly. In this division, all the assembled units meet the assembly conveyor at the point where they are needed. At the start of the track a front axle unit, a rear axle unit and a frame unit are assembled. This assembly is then started in motion by means of a chain conveyor, and as it moves down the room at a constant speed of eight feet per minute, each man adds one part to the growing chassis or does one operation, which is assigned to him, so that when the chassis reaches the end of the line, it is ready to run on its own power. ["The Story of an Automobile Factory," in "Universal Book of Knowledge and Wonders," 1917]
School sense, "gathering of all students for a presentation" is from 1932. From mid-14c. as "a gathering for deliberation," hence it is the name of the lower house in state (earlier colonial) legislatures in America (1680s). In 17c.-18c. assemblies "dancing balls 'among polite persons of both sexes,' often paid for by subscription of the participants" were a prominent feature of social life.
"assembly, council in a Middle Eastern land" (later, especially, with capital M-, the Persian national assembly), 1821, from Arabic majlis "assembly," literally "session," from jalasa "he sat down."
1590s, "open assembly place, chief public square and marketplace of a town; popular political assembly held in such a place," from Greek agora "an assembly of the People" (as opposed to a council of Chiefs); "the place of assembly; a marketplace" (the typical spot for such an assembly), from ageirein "to assemble," from PIE root *ger- "to gather." The Greek word also could mean "public speaking," and "things to be sold." For sense, compare Roman forum.
Old English þing "meeting, assembly, council, discussion," later "entity, being, matter" (subject of deliberation in an assembly), also "act, deed, event, material object, body, being, creature," from Proto-Germanic *thinga- "assembly" (source also of Old Frisian thing "assembly, council, suit, matter, thing," Middle Dutch dinc "court-day, suit, plea, concern, affair, thing," Dutch ding "thing," Old High German ding "public assembly for judgment and business, lawsuit," German Ding "affair, matter, thing," Old Norse þing "public assembly"). The Germanic word is perhaps literally "appointed time," from a PIE *tenk- (1), from root *ten- "stretch," perhaps on notion of "stretch of time for a meeting or assembly."
The sense "meeting, assembly" did not survive Old English. For sense evolution, compare French chose, Spanish cosa "thing," from Latin causa "judicial process, lawsuit, case;" Latin res "affair, thing," also "case at law, cause." Old sense is preserved in second element of hustings and in Icelandic Althing, the nation's general assembly.
Of persons, often pityingly, from late 13c. Used colloquially since c. 1600 to indicate things the speaker can't name at the moment, often with various meaningless suffixes (see thingamajig).
Things "personal possessions" is from c. 1300. The thing "what's stylish or fashionable" is recorded from 1762. Phrase do your thing "follow your particular predilection," though associated with hippie-speak of 1960s is attested from 1841.
"eulogy, laudation, praise bestowed upon some person, action, or character," c. 1600, from French panégyrique (1510s), from Latin panegyricus "public eulogy," originally an adjective, "for a public festival," from Greek panēgyrikos (logos) "(a speech) given in or addressed to a public assembly," from panēgyris "public assembly (especially in honor of a god)," from pan- "all" (see pan-) + agyris "place of assembly," Aeolic form of agora (see agora). Related: Panegyrical; panegyrist.