See posthaste in Webster's New World Roget's A-Z Thesaurus II
adverb
In a rapid way:
apace, fast, quick, quickly. (Informal) flat out, hell-for-leather, lickety-split, pronto. Idioms: full tilt, in a flash, in nothing flat, like a bat out of hell, like a blue streak, like a flash, like a house on fire, like a shot, like a streak, like greased lightning, like the wind, like wildfire. See fast
