sin), from PIE *es-ont- "being, existence," thus "real, true," from prp. of base *es-, the s-form of the verb "to be" (see
be), preserved in L. sunt "they are" and Ger. sind. Archaic in Eng., it is the root of modern words for "true" in Swed. (sann) and Dan. (sand). In common use until c.1650, then obsolete until revived as an archaism early 19c. by Scott, etc. Soothsayer is attested from 1340, from O.E. seðan "declare (the truth)."
sootheO.E. soðian "show to be true," from soð "true" (see
sooth). Sense of "quiet, comfort, mollify" is first recorded 1697, on notion of "to assuage one by asserting that what he says is true" (i.e. to be a yes-man), a sense attested from 1568.