by Jupiter

From Latin pro Iuppiter. Ellipsis of a full oath of the form "I swear by Jupiter that…". Originally a literal oath; later a minced oath.

by Jupiter

1. (obsolete, Classics) Invocation of the Greek god Jupiter.
   • 1820, Mitchell, Thomas, transl., “The Clouds”, in The Comedies of Aristophanes, volume 1, translation of Νεφέλαι Nephelai by Aristophanes, page 91:

     I see how it is with you. You are mad, / Stark mad, by Jupiter!

2. (dated, chiefly British) Minced oath for by God.
   • c. 1603–1606, Shakespeare, William, King Lear, act 1, scene 1, lines 178–179:

     Away! By Jupiter, / This shall not be revoked!

   • 1874 September 1, Burnett, Fannie Hodgson, “Pretty Polly Pemberton”, in Peterson's Magazine, volume 66, number 3, page 180:

     "By Jupiter!" employing his usual mild expletive, "look here, old fellow, had she a white dress on, and geranium-colored bows, and—"

• See Thesaurus:wow or Thesaurus:dammit

• by Jove