I’m guessing rarin’, as in ‘rarin’ to go’, comes from the verb rearing, as a horse would rear up. I assume it’s an American dialectical thing. (Texas/Oklahoma?)
Is ‘rearing to go’ an acceptable alternative?* Or is the phrase only used with rarin’?
I believe I have only really heard it in the idiomatic “rarin’ to go”, however. I’ve never heard anybody be, say, rarin’ to board a plane or rarin’ to order from the menu.
Anybody else ever heard “rare back” in preparation to strike someone? As in: “Jimmy said a cussword yesterday, and Mama just rared back and slapped him.”
Maybe it’s also a derivation of “rear”? I don’t have access to an OED today and the free online source was unhelpful.
This is in rural Deep South, USA. It was more common 30 years ago, though I still hear it now and then.