Dog noun the Greyhound bus line US,1974 A fixture in American travel until a crippling strike in the 1990s; variants include “Grey Dog” and “ol’ Grey Dog”.
— Gwyneth A. “Dandalion” Seese, TijuanaBearinaSmoke’UmUpTaix, p. 14, 1977
Well, the wife left me again. Took the ol’ Grey Dog to Falfurrias last night ... thank God. — Ken Weaver, TexasCrude, p. 110, 1984