The rolling of the sea in a storm [1400s]. Of a ship, to be tossed on the waves [1300s-1500s]. Of the stomach, to be upset or disturbed. [Hence] wally, of the sea, tempestuous [1500s-1700s], and walterer, one who overthrows [late 1300s-late 1500s].--Sir James Murray's New English Dictionary, 1928
Feast Eve of St. Elmo,
a patron of sailors. An eerie visual phenomenon, St. Elmo's fire -- also called a furole, dead fire, or friar's-lantern -- is occasionally seen as a glowing bluish electrical discharge atop a ship's mast or at the end of a yardarm before a storm. Sometimes known as a corposant or holy body, and mentioned by Shakespeare in The Tempest, it was believed to warn of a storm or even a shipwreck. But it was also seen as a sign by some that the ship enjoyed the divine protection of St. Elmo, who was invoked for deliverance from "the walters," or seasickness. Joseph Worcester's Dictionary of the English Language (1881) mentioned the related ignis-fatuus, which "flits about in the air a little above the surface of the earth, chiefly in marshy places or stagnant waters. From Latin ignis, fire, and fatuus, foolish."
And no, St. Elmo did not talk about himself in third person with an incredibly annoying squeaky baby voice. And he sure as heck didn't vibrate when you tickled him.