For words that have only 3 letters, there is no 4th letter. For example with the word “incorporate”, there isn't any a lot more letters afterwards and so needs to be the word "include". The word “addict” is inside the BIP39 wordlist however, you might have made use of “addi” https://socialstrategie.com/story4662553/little-known-facts-about-bip39-words