Definition of "posthaste" [post•haste]

• With great speed; rapidly. (adverb)
• Archaic Great speed; rapidity. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "A dozen miles to the north, the defeated Istarian army huddled against the outer walls of the city, awaiting reinforcements recalled posthaste from their stations along the Thoradin border."
• "Woody Harrelson, who asked for treatment "posthaste," she said."
• "When the legions had marched into camp outside Verona, Catulus Caesar knew the first thing he had to do was send word posthaste to Rome of the disaster up the Athesis; if he didn’t, he suspected Sulla would via Gaius Marius, so it was important that his be the first version Rome absorbed."