May have been a DAWG like this: https://www.cs.cmu.edu/afs/cs/academic/class/15451-s06/www/l...

These days GADDAG are used which are faster, but usually much less space efficient: https://en.wikipedia.org/wiki/GADDAG

Neither seem to work well in my attempts on this data as the words all being short and the same length work against it in these schemes.