"a thing," indefinitely, late Old English aniþing, from any + thing. But Old English ænig þinga apparently also meant "somehow, anyhow" (glossing Latin quoquo modo).
Entries linking to anything
any adj., pron.
"one, a or an, some," Old English ænig (adjective, pronoun) "any, anyone," literally "one-y," from Proto-Germanic *ainagas (source also of Old Saxon enig, Old Norse einigr, Old Frisian enich, Dutch enig, German einig), from PIE root *oi-no- "one, unique." The -y may have diminutive force here.
As a noun, late 12c.; as an adverb, "in any degree," c. 1400. Emphatic form any old______ (British variant: any bloody ______) is recorded from 1896. At any rate is recorded from 1847. Among the large family of compounds beginning with any-, anykyn "any kind" (c. 1300) did not survive, and Anywhen (1831) is rarely used, but OED calls it "common in Southern [English] dialects."
[A]ani refers to single entities, amounts, etc., occurring at random or chosen at random, as being convenient, suitable, to one's liking, etc. It is frequently emphatic and generalizing, having the force of 'any whatever, any at all' and 'any and every'. It is common in questions, conditional clauses, and negative statements, but not in affirmative statements (where som is used instead). [The Middle English Compendium]
thing n.
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.
anythingarian n.
"one indifferent to religious creeds, one 'that always make their interest the standard of their religion,'" 1704, originally dismissive, from anything on model of trinitarian, unitarian, etc.