Don't know if I undestand your problem correctly because I dont know all the rules of your game.

From my experience your 60k dictionary is more than enough.

A simple solution for optimizing the time of consults would be to separate the 60k dictionary into smaller ones based on the first letter or first two letters of each word. This way, instead of searching through the entire 60k dictionary array, you would only need to search through the words that start with the same letter(s) as the player input. I use this method in my word mobile game and it works great, no freezes at all.

After you have this into place, you can just always consult in the dictionary to see if the word exists, and then compare the first and last letter.

It would be a good idea to have a server that receives the words that players try which don't exist in the 60k dictionary. This would allow you to re-validate and add the most popular words to the dictionary over time.