• WordNet 3.6
    • v postmark stamp with a postmark to indicate date and time of mailing
    • n postmark a cancellation mark stamped on mail by postal officials; indicates the post office and date of mailing
    • ***
Webster's Revised Unabridged Dictionary
    • n Postmark The mark, or stamp, of a post office on a letter, giving the place and date of mailing or of arrival.
    • v. t Postmark To mark with a post-office stamp; as, to postmark a letter or parcel.
    • ***
Century Dictionary and Cyclopedia
    • n postmark The mark or stamp of a post-office placed on a letter, paper, card, or package sent through the mail; an official stamp on a letter, etc., giving the place and date of sending or the place and date of receipt.
    • postmark To affix the stamp or mark of the post-office to, as letters, etc.
    • ***
Chambers's Twentieth Century Dictionary
    • Postmark the mark or stamp put upon a letter at a post-office showing the time and place of reception and delivery
    • ***


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


In literature:

They were sitting at breakfast one morning when two letters were brought, both with foreign postmarks.
"Jack Harkaway's Boy Tinker Among The Turks" by Bracebridge Hemyng
Alfred knew by the postmark that they were from him.
"Watch Yourself Go By" by Al. G. Field
The postmark is almost obliterated.
"Grace Harlowe's Third Year at Overton College" by Jessie Graham Flower
It bore a Cornish postmark.
"Love Among the Chickens" by P. G. Wodehouse
And the postmark was London.
"The Borough Treasurer" by Joseph Smith Fletcher
Fougas recognized his own handwriting and the Berlin postmark, tore open the envelope, and displayed the check.
"The Man With The Broken Ear" by Edmond About
A letter arrived for my father yesterday evening, bearing the Fordingbridge postmark.
"The Strand Magazine, Volume V, Issue 28, April 1893" by Various
It was dated "Sunday," but bore no address further than "London, N." on the postmark.
"The Master of the Shell" by Talbot Baines Reed
Annie began brushing the armchair vigorously, and, as she worked, tried once more to see the postmark on the letter.
"The Easiest Way" by Eugene Walter and Arthur Hornblow
There was of course no postmark, as it had been sent by messenger; and she knew nothing of the handwriting.
"True to his Colours" by Theodore P. Wilson
It was one, though it bore no postmark.
"The Lone Ranche" by Captain Mayne Reid
It was postmarked New York and the date was four days back.
"Randy of the River" by Horatio Alger Jr.
That copy was anonymously mailed, bearing a New York postmark, and its sending was a puzzle which its recipient never solved.
"The Tyranny of Weakness" by Charles Neville Buck
They bore the postmarks of the old country.
"Charlie to the Rescue" by R.M. Ballantyne
The letter was postmarked at Beach Haven, and had been mailed the evening previous.
"The Rover Boys at Colby Hall" by Arthur M. Winfield
The crest on the paper, the postmark on the envelope, convinced him of its authenticity.
"The Lure of the Mask" by Harold MacGrath
It was postmarked Ithaca.
"The Rover Boys on the Farm" by Arthur M. Winfield (AKA Edward Stratemeyer)
There is only one letter, but this bears a suggestive postmark.
"Oswald Langdon" by Carson Jay Lee
But, when the postmark induced Maurice to start for Dresden, I saw what a fool I had been.
"Fairy Fingers" by Anna Cora Mowatt Ritchie
He looked at the postmark.
"Jack O' Judgment" by Edgar Wallace

In news:

Ballots must be received--not just postmarked--by Tuesday, November 7 to be valid.
Ballots for the primary must be postmarked or dropped off at designated sites by 8 pm today.
The letter to The Associated Press was dated July 14 and postmarked July 17.
Montgomery said that his financial disclosure form was mailed Tuesday and has a Sept 4 postmark on the envelop.
Mail-in ballots postmarked by tomorrow will be accepted as late as November 19th.
Postmark deadline for our annual fiction contest is Monday, Dec 10.
Early Registration Fees (Postmarked by Jan 15, 2010).
Registration for the conference is $80, includes lunch and must be postmarked by Oct 29.
In order to register via mail, a registration application needs to be postmarked by today.
The letter , according to police, is postmarked from Phoenix, Ariz.
A Dec 31st postmark is the latest that will be accepted without a penalty.
Ballots returned by mail must also be postmarked no later than Dec 3.
Postal Service offers North Pole postmarks.
For folks who would like a special " North Pole " postmark on their mail, the US Postal Service is once again offering the free service, according to a press release.
For folks who would like a special "North Pole" postmark on their mail, the US Postal Service is once again offering the free service, according to a press release.

In science:

The inventor's practice of publishing an invention, or putting it in a self-addressed envelope and getting it postmarked, to prove the invention originated no later than a certain day.
Improvements to time bracketed authentication