• fiddyup,
• viddyup,
• biddyup,
• hiddyup,
• yiddyup,
• tiddyup,
• guddyup,
• gjddyup,
• gkddyup,
• goddyup,
• g9ddyup,
• g8ddyup,
• gisdyup,
• gixdyup,
• gicdyup,
• gifdyup,
• girdyup,
• giedyup,
• gidsyup,
• gidxyup

• getty,
• Gitter up,
• Kiddie up,
• Kitty up,
• get up,
• Getty up,
• giddyap,
• giddy.

The plural form of "giddyup" is still "giddyup." The word does not change when pluralized.

The word "giddyup" does not have a singular form. It is already a single-word imperative phrase used as a command to make a horse start moving or go faster.