also adv., conj.

Old English eall "every, entire, the whole quantity of" (adj.), "fully, wholly, entirely" (adv.), from Proto-Germanic *alnaz (source also of Old Frisian, Old High German al; German all, alle; Old Norse allr; Gothic alls), with no certain connection outside Germanic. As a noun, in Old English, "all that is, everything."

Combinations with all meaning "wholly, without limit" were common in Old English (such as eall-halig "all-holy," eall-mihtig "all-mighty") and the habit has continued. Middle English had al-wher "wherever; whenever" (early 14c.); al-soon "as soon as possible," al-what (c. 1300) "all sorts of things, whatever."

Of the common modern phrases with it, at all "in any way" is from mid-14c., and all "and everything (else)" is from 1530s, all but "everything short of" is from 1590s. First record of all out "to one's full powers" is by 1880. All clear as a signal of "no danger" is recorded from 1902. All right, indicative of assent or approval, is attested by 1837; the meaning "satisfactory, acceptable" is by 1939, from the notion of "turning out well."

The use of a, a' as an abbreviation of all (as in Burns' "A Man's a Man for A' that") is a modern Scottishism but has history in English to 13c.

Middle English so, from Old English swa, swæ (adv., conj., pron.) "in this way, in such a manner that," also "to that extent; so as, consequently, therefore," and purely intensive; from Proto-Germanic *swa (source also of Old Saxon, Middle Dutch, Old High German so, Old Norse sva, Danish saa, Swedish så, Old Frisian sa, Dutch zo, German so "so," Gothic swa "as"), from PIE reflexive pronominal stem *swo- "so" (source also of Greek hos "as," Old Latin suad "so," Latin se "himself"), derivative of *s(w)e-, pronoun of the third person and reflexive (see idiom).

Old English swa frequently was strengthened by eall, and so also is contained in compounds as, also, such. The -w- was crushed out by contraction from 12c.; compare two, which underwent the same process but retained its spelling.

As a word confirming a previous statement, late Old English; also from late Old English as an intensive in an affirmative clause (such as so very "exceedingly, extremely"). As an "introductory particle" [OED] from 1590s. Used to add emphasis or contradict a negative from 1913. So in mid-20c. British slang could mean "homosexual" (adj.).

So? as a term of dismissal is attested from 1886 (short for is that so?, etc.); it is older as an abbreviation of is it so? (1803). So what as an exclamation of indifference dates from 1934.

The abbreviating phrase and so forth is attested in Old English; and so on is attested from 1724. So far "at such a distance" was in Middle English; so far so good is from 1721, said then to be a Scottish proverb.