as indicated by the classification as "experimental" , the
definition end point  is at a very early point of its development.
The mobile app team has added preliminary support for extracting
definitions in the content service  using Parsoid's template
metadata, and is using this end point to power a "define this word"
feature in the next version of the Android app. You can preview the
feature in the beta Android app when browsing English Wikipedia by
selecting a word, and then hitting the 'definition' icon next to
In this first iteration, only English Wiktionary is supported.
Generalizing the service and API end point to provide definitions
using more or all Wiktionaries will require more work and planning. In
the next iteration, I would expect a focus on enabling collaborative
definition and maintenance of extraction rules, as well as broader
involvement of Wiktionary communities in the planning process. The
timing for the next iteration depends partly on the mobile app team's
priorities, so I will defer to the team to comment on this.
To summarize: We are aiming to gradually develop this into a generally
useful, stable and well-documented API entry point for word
definitions. The experimental end point published right now is just
the beginning, and you are very much invited to help shape the way
Principal Engineer, Wikimedia Foundation