Response from Kory
We have a page on our premium Web site, www.Merriam-WebsterUnabridged.com, where users can submit citations to us. You can use the Day Pass promotion to gain 24-hours of free access to MWU after viewing an ad; click on the "Free premium access" box on our home page, and once you are on the site, click on the "Submit a Word" link directly below our logo. I would encourage this route as the citation is automatically formatted per our particular citational style. Anything you sent me would have to be reformatted and typed in again.
Below you will find the very extensive FAQ from MWU about what we need for our citations. The foremost requirement is that the source material be edited, printed, and published (on paper, not electronically). There are a number of other things we need, but you can read the FAQ to find the rest of the information.
Thanks for your interest in Merriam-Webster.
Kory Stamper, Associate Editor