by jingo

Uncertain for a long time. Main theories include:

• a minced oath of "by Jesus";[1] compare crikey, zounds, egads, etc.
• a corruption ultimately of "by St. Gingoulph", in reference to Saint Gangulphus of Burgundy.[2]
• a borrowing from Basque Jinkoa (“god”); compare by Jove.[1] Basque sailors ― a common famous occupation for their people, who often swore by their term for God ― travelled far through the seas for centuries, and often met Englishmen.

by jingo

1. Used to express determination or surprise.

   Synonyms: see Thesaurus:wow

   • 1694, François Rabelais, chapter XXVI, in Peter Anthony Motteux, transl., The fifth book of The works of Francis Rabelais, M.D. […] ‎, page 145:

     […] of all commend me to Ball, this is the Friar of the World, for my Money; you've heard how short, concise, and compendious he is in his Answers? Nothing is to be got out of him but Monosyllables; by Jingo, I believe he would make three bits of a Cherry.

   • 1909, Booth Tarkington, Beasley's Christmas Party, New York: Harper & Brothers, pages 22–23:

     “Yes, I'll make Simpledoria get out of the way. Come here, Simpledoria. Now, Bill, put your heels together on the edge of the walk. That's right. All ready? Now then! One for the money—two for the show—three to make ready—and four for to GO!” Another silence. “By jingo, Bill Hammersley, you've beat me! Ha, ha! That was a jump! What say?”

   • 1989, Moonlighting:

     You can't tell the difference between surface and substance. Between celebrity and real accomplishment. By jingo, you're right. The scales have fallen from my eyes and I owe it all to you.