1st solution:
This is simple, if you need help you can use a solver like this one:
http://wordfinder.yourdictionary.comThe page will show you most of the possible words, including the 8-letter word.
2nd solution:
Simply, keep playing a game until you unlock the Hint Button (the owl). You can track your progress in the hint bar. Then click it and the game will show you the longest word.
Works with:
(Sorry for my English
)