Source : Webster's Revised Unabridged Dictionary (1913)

Postmark \Post"mark`\, n.
   The mark, or stamp, of a post office on a letter, giving the
   place and date of mailing or of arrival.

Postmark \Post"mark`\, v. t. [imp. & p. p. {Postmarked}; p. pr.
   & vb. n. {Postmarking}.]
   To mark with a post-office stamp; as, to postmark a letter or
   parcel.

Source : WordNet®

postmark
     n : a cancellation mark stamped on mail by postal officials;
         indicates the post office and date of mailing
     v : stamp with a postmark to indicate date and time of mailing
         [syn: {frank}]