so-called (adj.)

mid-13c., "cry out; call for, summon, invoke; ask for, demand, order; give a name to, apply by way of designation," from Old Norse kalla "cry loudly, summon in a loud voice; name, call by name," from Proto-Germanic *kall- (source also of Middle Dutch kallen "speak, say, tell," Dutch kallen "to talk, chatter," Old High German kallon "speak loudly, call"), from PIE root *gal- "to call, shout." Related: Called; calling.

Old English cognate ceallian "to shout, utter in a loud voice" was rare, the usual word being clipian (source of Middle English clepe, yclept). Old English also had hropan hruofan, cognate of German rufen.

The "heads-or-tails" coin-toss sense is from 1801; the card-playing sense "demand that the hands be shown" is from 1670s; the specific poker sense of "match or raise a bet" is by 1889. The meaning "make a short stop or visit" (Middle English) was literally "stand at the door and call." The "attempt a telephone connection with" sense is from 1882.

To call for "demand, require" is from 1530s (earlier in this sense was call after, c. 1400). To call (something) back "revoke" is from 1550s. To call (something) off "cancel" is by 1888; earlier call off meant "summon away, divert" (1630s). To call (someone) names is from 1590s. To call out someone to fight (1823) corresponds to French provoquer. To call it a night "go to bed" is from 1919.

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.