[1] : The Collaborative International Dictionary of English v.0.48

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.
   1913 webster

[2] : The Collaborative International Dictionary of English v.0.48

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.
   1913 webster
see also:
postmarked postmarking 

[3] : WordNet (r) 2.0

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
see also:
frank 

Postmark >> P Words
Postmark, definition of term: Postmark
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