O.E.
þing "meeting, assembly," later "entity, being, matter" (subject of deliberation in an assembly), also "act, deed, event, material object, body, being," from P.Gmc.
*thengan "appointed time" (cf. O.Fris.
thing "assembly, council, suit, matter, thing," M.Du.
dinc "court-day, suit, plea, concern, affair, thing," Du.
ding "thing," O.H.G.
ding "public assembly for judgment and business, lawsuit," Ger.
ding "affair, matter, thing," O.N.
þing "public assembly"). Some suggest an ultimate connection to PIE root
*ten- "stretch," perhaps on notion of "stretch of time for a meeting or assembly." For sense evolution, cf. Fr.
chose, Sp.
cosa "thing," from L.
causa "judicial process, lawsuit, case;" L.
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. Southern U.S. pronunciation
thang attested from 1937.
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. Used colloquially since 1602 to indicate things the speaker can't name at the moment, often with various meaningless suffixes, e.g.
thingumbob (1751),
thingamajig (1824).
[ting] 
