posthaste

adv

1. (dated, formal, not-comparable)Quickly, as fast as someone travelling post; with great speed.

   “It is imperative that you finish your task posthaste.”

   “"Sasi cannot last through the night." These words from his physician, and the spectacle of my friend, now reduced almost to a skeleton, sent me posthaste to Serampore.”

noun

1. (alt-of, alternative, uncountable)Alternative spelling of post-haste.

   “"And this, I take it, Is the main motive of our preparations The source of this our watch, and the chief head Of this post-haste and rummage in the land."”