Word Origin & History
"mindless, gung-ho patriot," 1878, picked up from the refrain of a music hall song written by G.W. Hunt supporting aggressive British policy toward Russia at a time of international tension. ("We don't want to fight, But by Jingo! if we do, We've got the ships, we've got the men, We've got the money
too.") As an asseveration, it was in colloquial use since 1694, and is apparently yet another euphemism for Jesus, influenced by conjurer's gibberish presto-jingo (1670). The suggestion that it somehow derives from Basque Jinko "god" is "not impossible," but "as yet unsupported by evidence" [OED].