Giddap

gid·dy·up

 (gĭd′ē-ŭp′) also gid·dy·ap (-ăp′, -ŭp′) or gid·dap (gĭ-dăp′, -dŭp′)
interj.
Used to command a horse to go ahead or go at a faster pace.

[Alteration of get up.]

giddap

(ɡɪˈdæp) or

giddy-up

interj
an exclamation used to make a horse go faster
[C20: colloquial form of get up]

Giddap

Command to a horse to start or to move faster.