I too wrote a similar app for my personal problem and also served to be a good way to learn about kotlin and Android ecosystem. I also tried a rewrite in flutter and compose. The idea was to use select the word and then click meaning from context menu so that meaning occurs as notification and disappears in 15 seconds. I used Wiktionary as dataset source and app works offline.
https://play.google.com/store/apps/details?id=com.xtreak.not...
https://github.com/tirkarthi/NotificationDictionary