Dictionary built into the app

Many times, when I am using Khan Academy in the mobile app or a mobile browser, I will come across some vocabulary I do not know. This forces me to exit the app or open a new tab and search for it, which is inconvenient.

Adding a dictionary to make this easier would greatly improve the user experience, especially in the app but also on mobile browsers, such as is present in Google Books or in the Kindle e-reader. My idea of a dictionary would show a definition of any words highlighted in the mobile app or browser.

It may not be feasible considering deciding which dictionaries to use or what to include (context? history?) or even whether it is allowed legally to use those dictionaries, but if it was possible to include one, dictionaries would be an extremely useful feature on the mobile version of Khan Academy.