soothyoudaoicibaDictYouDict
sooth: [OE] Sooth ‘truth’ (which now survives in current usage only in the compound soothsayer [14]) goes back ultimately to Indo-European *sntyós (possible ancestor also of English sin). This was a derivative of the base *es- ‘be’, and hence etymologically means ‘that which is’. It passed into prehistoric Germanic as the adjective *santhaz.

As in English, in most other Germanic languages the word has now died out, but it survives in Swedish (sann) and Danish (sand) as an adjective meaning ‘true’. From the Old English form sōth a verb was formed, sōthian ‘prove to be true’, which has evolved into modern English soothe. Its present-day meaning did not emerge, via intermediate ‘confirm’ and ‘please or flatter by confirming or agreeing’, until the 17th century.
=> soothe
sin (n.)youdaoicibaDictYouDict
Old English synn "moral wrongdoing, injury, mischief, enmity, feud, guilt, crime, offense against God, misdeed," from Proto-Germanic *sun(d)jo- "sin" (cognates: Old Saxon sundia, Old Frisian sende, Middle Dutch sonde, Dutch zonde, German Sünde "sin, transgression, trespass, offense," extended forms), probably ultimately "it is true," i.e. "the sin is real" (compare Gothic sonjis, Old Norse sannr "true"), from PIE *snt-ya-, a collective form from *es-ont- "becoming," present participle of root *es- "to be" (see is).

The semantic development is via notion of "to be truly the one (who is guilty)," as in Old Norse phrase verð sannr at "be found guilty of," and the use of the phrase "it is being" in Hittite confessional formula. The same process probably yielded the Latin word sons (genitive sontis) "guilty, criminal" from present participle of sum, esse "to be, that which is." Some etymologists believe the Germanic word was an early borrowing directly from the Latin genitive. Also see sooth.

Sin-eater is attested from 1680s. To live in sin "cohabit without marriage" is from 1838; used earlier in a more general sense. Ice hockey slang sin bin "penalty box" is attested from 1950.