Save definitions on Android
Once you look up the definition of a word, tap on the star icon at the top right corner of your screen. Once it turns blue, it is certain that the word has been saved in your "Favourites list.
Save definitions on iOS
Once you look up the definition of a word, tap on the "Heart" icon that is located at the bottom of the definition. As it turns blue, it means that the definition is now listed in your "Favourites" section.
To check your "Favourites" list up, please tap on the other "Heart" icon at the bottom right corner of your screen.