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

mailbag \mail"bag`\, mail bag \mail bag\n.
   a bag in which mailed matter is conveyed or shipped under
   public authority.

   syn: mail pouch.
        wordnet 1.5

   2. a letter carrier's shoulder bag; as, in england they call
      a mailbag a postbag.

   syn: postbag.
        wordnet 1.5 mailboat

[2] : WordNet (r) 2.0

mailbag
     n 1: pouch used in the shipment of mail syn: mail pouch
     2: letter carrier's shoulder bag; "in england they call a
        mailbag a postbag" syn: postbag
see also:
mail pouch postbag 

Mailbag >> M Words
Mailbag, definition of term: Mailbag
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