Sometimes the API the app talks to is unable to return a definition, or the definition it returns is unhelpful (i.e. with names like "Catullus"). Being able to add your own would allow users to get around this problem, and even add exceptions to what the API thinks the possible inflections should be.
If you make changes to a word's Definition.entries[] and call updateDefinitionView() on the word, the app will successfully use the changed Definition.entries[] when it updates tables and whatnot.
Sometimes the API the app talks to is unable to return a definition, or the definition it returns is unhelpful (i.e. with names like "Catullus"). Being able to add your own would allow users to get around this problem, and even add exceptions to what the API thinks the possible inflections should be.