The origins are straightforward: a soothsayer is someone who says sooth. You may, however, find that less than enlightening! Sooth is an archaic word meaning "truth" or "reality" that dates from Old English and was used until about the first half of the 17th century. (It is believed to share an ancestor with words suggesting truthfulness and reality in Old Norse, Greek, Old High German, Sanskrit, Latin, and Gothic languages.) Soothsayer itself has been documented in print as far back as the 14th century. Today, it is also a moniker of the insect the mantis, whose name means "prophet" in Greek.