• Webster's Revised Unabridged Dictionary
    • n Posthaste Haste or speed in traveling, like that of a post or courier.
    • adv Posthaste With speed or expedition; as, he traveled posthaste; to send posthaste.
    • ***
Century Dictionary and Cyclopedia
    • n posthaste Haste or speed like that of a post or courier in traveling.
    • posthaste With the haste of a post; with speed or urgent expedition: as, he traveled post-haste.
    • posthaste Expeditious; speedy; immediate.
    • posthaste [The edition of 1623 reads “post, post-haste.”]
    • ***
Chambers's Twentieth Century Dictionary
    • n Posthaste haste in travelling like that of a post
    • ***


Chambers's Twentieth Century Dictionary
Fr. poste—L. ponĕre, positum, to place.


In literature:

Pierre took the buggy and drove posthaste to town for a doctor.
"The Ruling Passion" by Henry van Dyke
Didn't she send me posthaste with an umbrella 'cause she see a little cloud in the sky?
"Pollyanna" by Eleanor H. Porter
He sent posthaste for reinforcements.
"Captains of the Civil War" by William Wood
It was as Rolfe had said, and the free and able-bodied of the plantations had put out, posthaste, for matrimony.
"To Have and To Hold" by Mary Johnston
So he went up to the stables and sent Pat posthaste back to his father.
"Seven Little Australians" by Ethel Sybil Turner
He accordingly sent his private secretary Biraga, posthaste to Spain with two letters.
"History of the United Netherlands, 1600-09, Vol. IV. Complete" by John Lothrop Motley
Gayangos was sent back to Spain posthaste.
"A Writer's Recollections (In Two Volumes), Volume II" by Mrs. Humphry Ward
The Nord Express had brought me posthaste across Europe from Petersburg to Calais, and I was again in London.
"The Czar's Spy" by William Le Queux
It appears he got a fortnight's leave, and came posthaste to London to find you.
"Molly Bawn" by Margaret Wolfe Hamilton
To Inis Glora he went, posthaste, himself.
"A Book of Myths" by Jean Lang
First he took the Record with him, and travelled posthaste to Chalons, where he asked de Lery to take him to their relative, de Villerai.
"The False Chevalier" by William Douw Lighthall
He had consented; he had returned posthaste.
"Fibble, D. D." by Irvin Shrewsbury Cobb
As soon as it was daylight, Mrs. Washington sent a messenger posthaste for Dr. Craik.
"Seaport in Virginia" by Gay Montague Moore
He knew then that there could be but one answer, and he headed for the control room posthaste.
"A Knyght Ther Was" by Robert F. Young
A messenger from Red Range had come posthaste for some merchandise.
"The Price of the Prairie" by Margaret Hill McCarter
From Second Westings that morning, after old Debby's alarm, Doctor John and Doctor Jim had came posthaste on horseback to Westings Landing.
"Barbara Ladd" by Charles G. D. Roberts
Other sections sent in committees during the day, and as a result of all Governor Sayers ordered posthaste shipments of supplies.
"The Complete Story of the Galveston Horror" by Various
Gaston, the hero of the tale, had ridden posthaste from Paris to save his fellows.
"Dumas' Paris" by Francis Miltoun
James Borden had come posthaste from London, acting upon an impulse which had swept him off his feet.
"The Wicked Marquis" by E. Phillips Oppenheim
To-morrow morning, at daybreak, you depart alone, posthaste, to liberate Bernard de Rohan.
"Corse de Leon, Volume I (of 2)" by G. P. R. James

In news:

My impression of Eastwood's acting is not subtle: Dude needs to hang it up, posthaste.
Professional chef, Festivals Acadiens et Créoles bigwig and modern day Renaissance man Pat Mould dives into the Posthaste ring for a few rounds of verbal jamicide.
The excellent biography of Django by Michael Dregni has been released in paperback, so jazz-guitar fans who haven't read it yet have no excuse for not devouring it posthaste.