so (adv.)

Old English swa, swæ (adv., conj., pron.) "in this way," 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 , 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 eliminated 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.). So what as an exclamation of indifference dates from 1934. Abbreviating phrase and so on is attested from 1724. So far so good is from 1721.

Definitions of so
so (adv.)
to a very great extent or degree;
I love you so
never been so happy
my head aches so!
the idea is so obvious
so (adv.)
in a manner that facilitates;
he observed the snakes so he could describe their behavior
he stooped down so he could pick up his hat
so (adv.)
in such a condition or manner, especially as expressed or implied;
so live your life that old age will bring no regrets
They're happy and I hope they will remain so
so (adv.)
to a certain unspecified extent or degree;
I can only go so far with this student
can do only so much in a day
so (adv.)
in the same way; also;
I was offended and so was he
worked hard and so did she
so (adv.)
in the way indicated; (`thusly' is a nonstandard variant);
hold the brush so
Synonyms: thus / thusly
so (adv.)
(usually followed by `that') to an extent or degree as expressed;
he was so tired he could hardly stand
so dirty that it smells
so (adv.)
subsequently or soon afterward (often used as sentence connectors);
and so home and to bed
Synonyms: then / and so
so (adv.)
(used to introduce a logical conclusion) from that fact or reason or as a result;
the witness is biased and so cannot be trusted
Synonyms: therefore / hence / thence / thus
so (adv.)
in truth (often tends to intensify);
he did so do it!
Synonyms: indeed
so (n.)
the syllable naming the fifth (dominant) note of any musical scale in solmization;
Synonyms: sol / soh