1. The mark or stamp of a post-office on a letter.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• postback,
• costmari,
• postarn,
• oostmark,
• lostmark,
• -ostmark,
• 0ostmark,
• pistmark,
• pkstmark,
• plstmark,
• ppstmark,
• postmak,
• postmaark,
• postmarker,
• postamus,
• Postmarx,
• Postfracka,
• Postfarca,
• postmkars,
• Postiack

• Postum,
• postmortem,
• postman,
• postma,
• postmaster.

The adverb form of "postmark" is "postmarked".

The adjective form of the word "postmark" is "postmarked".

The plural of the "postmark" can be the "postmarks".

The singular of the "postmark" can be the "postmark".