around (adv.)

prefix or inseparable particle, a relic of various Germanic and Latin elements.

In words derived from Old English, it commonly represents Old English an "on, in, into" (see on (prep.)), as in alive, above, asleep, aback, abroad, afoot, ashore, ahead, abed, aside, obsolete arank "in rank and file," etc., forming adjectives and adverbs from nouns, with the notion "in, at; engaged in." In this use it is identical to a (2).

It also can represent Middle English of (prep.) "off, from," as in anew, afresh, akin, abreast. Or it can be a reduced form of the Old English past participle prefix ge-, as in aware.

Or it can be the Old English intensive a-, originally ar- (cognate with German er- and probably implying originally "motion away from"), as in abide, arise, awake, ashamed, marking a verb as momentary, a single event. Such words sometimes were refashioned in early modern English as though the prefix were Latin (accursed, allay, affright are examples).

In words from Romanic languages, often it represents reduced forms of Latin ad "to, toward; for" (see ad-), or ab "from, away, off" (see ab-); both of which by about 7c. had been reduced to a in the ancestor of Old French. In a few cases it represents Latin ex.

[I]t naturally happened that all these a- prefixes were at length confusedly lumped together in idea, and the resultant a- looked upon as vaguely intensive, rhetorical, euphonic, or even archaic, and wholly otiose. [OED]

c. 1300 (early 13c. as a surname), "spherical in shape; circular in outline," of persons or animals, "well-fed;" from Anglo-French rounde, Old French roont (12c., Modern French rond), probably originally *redond, from Vulgar Latin *retundus (source also of Provençal redon, Spanish redondo, Old Italian ritondo), from Latin rotundus "like a wheel, circular, round," related to rota "wheel" (see rotary). The French word is the source of Middle Dutch ront (Dutch rond), Middle High German runt (German rund) and similar words in the Germanic languages. 

As an adverb from c. 1300. As a preposition from c. 1600, "so as to make a complete circuit" (as in round the world); 1715 as "throughout, all through" (as in round the clock); by 1743 as "so as to make a turn or partial circuit about" (as in round the corner). In many cases it is a shortened form of around (adv.).

Of numbers from mid-14c., "entire, full, complete, brought to completion," with the notion of symmetry extended to that of completeness. Round number for one only approximately correct, usually expressed in 10s, 100s, etc., is by 1640s. Compare round (v.). Round trip "an outward and return journey" is by 1844, originally of railways. A round-dance (1520s) is one in which the dancers move in a circle or ring. Round heels attested from 1926, in reference to incompetent boxers, 1927 in reference to loose women, implying in either case a tendency to end up flat on one's back.