A GADDAG[1] is a combination pre-/suffix trie that's used for move generation in Scrabble. Unlike a traditional dictionary to find anagrams for words, a GADDAG makes it easier to identify plays based off of available letters already on the board. I made a little visualization of how they work for a data visualization class a few years back.[2]

[1] https://en.wikipedia.org/wiki/GADDAG [2] https://www.axioms.me/gaddag/#?page-5