6 letter word who's letters cant be used to make any other words?

wanted to add that the letters cant be combined to make a 3 letter word. I was also wondering if someone knew the longest word those letters cant be used to make a 3 letter word. I am asking this because I like to push my son in his learning and thought this could be an extra credit type thing for him and I dont have the time to look and find these words in the dictionary myself.

thank you robink I knew there would be words out there that werent normally used word or everyday words. I want my son to really scour the dictionary to find words and this is something just what I was looking for

petunia b thank you too for trying