exclamation of surprise, 1895, probably euphemistic for Jesus. Form gee whiz is attested from 1871; gee whillikens (1851) seems to be the oldest form. As a command to a horse to go, 1620s, Scottish. It had a particular sense as a teamster's command: "go to the right (or off) side of the driver." Extended form gee-up is from 1733, the second element said by OED to be hup.
updated on February 24, 2015