define: <word> that Google shows at the top of the page is a type of Google one box. Google shows these special displays at the top of the search results for things like searches for:
Google does not use microdata to power one boxes. Rather it chooses the sites to feature manually and writes code to do so.
The only ways to get your site featured in the
define: one box for your language would be:
- Contact Google and get through to the right engineer (a very difficult prospect)
- Hope that when Google rolls this feature out to your language, that you site is one of the top dictionaries and is found by the the engineers at Google that are implementing this feature.
Dictionary definitions have semantic markup built into HTML. This is one of the few cases of semantic tags that have been in HTML since its earliest days. Because semantic tags exist in HTML itself, there is no schema.org markup for dictionary definitions. Use the following tags:
<dl> - Definition list
<dt> - Defined term
<dd> - Dictionary definition
For more information, see this excellent article.