Dictionary — ontologydriven

posthaste en · ADV

From the former instruction on letters ‘haste, post, haste’, later reinterpreted as a compound of post + haste.

(dated, formal, not-comparable) Quickly, as fast as someone travelling post; with great speed.
- "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. 1946, Paramahansa Yogananda, “Chapter 17”, in Autobiography of a Yogi:
- It is imperative that you finish your task posthaste.

Spelling	Labels	Source
postehaste	alternative, archaic	lexicographic
post haste	alternative	lexicographic
post-haste	alternative	lexicographic
poste-haste	alternative, archaic	lexicographic

quickly (quickly) · ASAP (quickly)

From the former instruction on letters ‘haste, post, haste’, later reinterpreted as a compound of post + haste.

(alt-of, alternative, uncountable) Alternative spelling of post-haste.
alt 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." c. 1599–1602 (date written), William Shakespeare, “The Tragedie of Hamlet, Prince of Denmarke”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, →OCLC, (please specify the act number in uppercase Roman numerals), page 1, lines 103-106:

Spelling	Labels	Source
poste-haste	alternative, archaic	lexicographic
postehaste	alternative, archaic	lexicographic
post haste	alternative	lexicographic
post-haste	alternative	lexicographic