Merriam-Webster's Dictionaries are available for most mobile platforms.
I noticed this when updating my eGames hotlist. There is a good selection of word games offered by Merriam-Webster Online. When I started exploring the site to see what was new, I noticed the Visual Dictionary and searched for school library and library. University shows up as a part of a downtown cityscape. Image downloads for educational, non-profit, and individula blogs are free, as long as the site http://www.visualdictionaryonline.com/ is clearly identified and linked. Kudos to Merriam-Webster for the Cool Tools!