Origin and history of thereabouts

suffix forming the genitive or possessive singular case of most Modern English nouns; its use gradually was extended in Middle English from Old English -es, the most common genitive inflection of masculine and neuter nouns (such as dæg "day," genitive dæges "day's"). The "-es" pronunciation is retained after a sibilant.

Old English also had genitives in -e, -re, -an, as well as "mutation-genitives" (boc "book," plural bec), and the -es form never was used in plural (where -a, -ra, -na prevailed), thus avoiding the verbal ambiguity of words like kings'.

In Middle English, both the possessive singular and the common plural forms were regularly spelled es, and when the e was dropped in pronunciation and from the written word, the habit grew up of writing an apostrophe in place of the lost e in the possessive singular to distinguish it from the plural. Later the apostrophe, which had come to be looked upon as the sign of the possessive, was carried over into the plural, but was written after the s to differentiate that form from the possessive singular. By a process of popular interpretation, the 's was supposed to be a contraction for his, and in some cases the his was actually "restored." [Samuel C. Earle, et al, "Sentences and their Elements," New York: Macmillan, 1911]

As a suffix forming some adverbs, it represents the genitive singular ending of Old English masculine and neuter nouns and some adjectives.

Middle English aboute, from Old English abutan (adv., prep.), earlier onbutan "on the outside of; around the circumference of, enveloping; in the vicinity of, near; hither and thither, from place to place," also "with a rotating or spinning motion," in late Old English "near in time, number, degree, etc., approximately;" a compound or contraction of on (see on; also see a- (1)) + be "by" (see by) + utan "outside," from ut (see out (adv.)).

By c. 1300 it had developed senses of "around, in a circular course, round and round; on every side, so as to surround; in every direction;" also "engaged in" (Wist ye not that I must be about my Father's business?), and gradually it forced out Old English ymbe, ymbutan (from PIE root *ambhi- "around") in the sense "round about, in the neighborhood of."

From mid-13c. as "in the matter, in connection with." From early 14c. as "in partial rotation, so as to face in a different direction." From late 14c. as "near at hand, about one's person." "In a circuitous course," hence "on the move" (late 13c.), and in Middle English "be about to do, be busy in preparation for," hence its use as a future participle in (to be) about to "in readiness, intending." Abouts (late 14c.), with adverbial genitive, still found in hereabouts, etc., probably is a northern dialectal form.

To bring about "cause or effect" and to come about "happen" are from late 14c. About face as a military command (short for right about face) is first attested 1861, American English.

Old English þær "in or at that definite place;" also "so far as, provided that, in that respect" (as to say "at that point of progress or proceeding"); from Proto-Germanic *thær (source also of Old Saxon thar, Old Frisian ther, Middle Low German dar, Middle Dutch daer, Dutch daar, Old High German dar, German da, Gothic þar, Old Norse þar). This is reconstructed to be from PIE *tar- "there" (source also of Sanskrit tar-hi "then"), from root *to- (see the) + adverbial suffix *-r.

Use as an indefinite grammatical subject (a fool there was) dates to Old English. Interjectional use to call attention to something ("like that!") is recorded from 1530s, variously emphasizing certainty, encouragement, or consolation. There, there as an expression of consolation is attested by 1872.

In brusque or casual address (hey, there; you, there) it is attested by 1580s. There he (or she) goes, calling attention to a way of acting, talking, etc., is by 1780. There it is expressing simplicity or consummation is by 1857.

That there as an emphatic of that is attested by 1742, a colloquial pleonasm, as though that (one) there; New England dialectal pronunciation at air (with em air) is by 1835. To have been there "had previous experience of (some activity)" is recorded from 1877. To be all there (colloquial) "have one's faculties or wits" is by 1864.