Green’s Dictionary of Slang

1. (US) a racehorse.

1938

D. Runyon ‘The Lemon Drop Kid’ in Runyon on Broadway (1954) 379: The giddy-aps are now running.

2. (orig. US, also giddy-up, gitty-up) the beginning; usu. in phr. (right) from the giddyap, straight from...

1974		R. Carter Sixteenth Round (1991) 71: Come on out here, and let’s me and you start from the giddy-up!
1975		E. Torres Carlito’s Way 124: The jury was dry-humped from the giddy-ap.
1984		W.J. Caunitz One Police Plaza 320: Look, scummer! [...] I’m tellin you right from the giddyap that we know all about your hit team.
1988		D. Woodrell Muscle for the Wing 97: Let’s get it right straight from the giddy-up.
1992		R. Price Clockers 505: Right from the gitty-up – did you kill Darryl Adams?
1995		L. Stavsky et al. A2Z.
2000		P. Beatty Tuff 59: I was lost from the giddy-up. Trying to read that shit was like trying to find Whitey at a hockey game.
2004		R.G. Barrett Rosa Marie’s Baby (2013) [ebook] [F]rom the ‘giddy-up’ it was obvious there was no love lost between the two gangs.

3. (US) energy, enthusiasm.

2010		L. Berney Gutshot Straight [ebook] [H]e’d never have the giddyup to start his own restaurant.
2010		W.D. Myers Cruisers 39: When people are facedown with a bloody lip [...] they will get the idea that they need to put some giddyap in their listen up.