1. One that uses the mails: large commercial mailers.
2. One who addresses, stamps, or otherwise prepares mail.
3. A container, such as a cardboard tube, used to hold material to be mailed: a cardboard book mailer.
4. An advertising leaflet included with a letter.

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.