and Gee-woo! addressed to horses both mean “Horse, get on.” Gee = horse. In Notts and many other counties nurses say to young children, “Come and see the gee-gees.” There is not the least likelihood that Gee-woo is the Italian gio, because gio will not fit in with any of the other terms, and it is absurd to suppose our peasants would go to Italy for such a word. Woa! or Woo! (q.v.), meaning stop, or halt, is quite another word. We subjoin the following quotation, although we differ from it. (See Come Ather.)
“Et cum sic gloriaretur, et cogitares cum quanta gloria duceretur ad illum virum super equum, dicendo Gio! Gio! cepit pede percutere terram quasi pungeret equum calcaribus.” —Dialogus Creaturarum (1480).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894