For words that only have three letters, there's no 4th letter. As an example with the word “include”, there isn't any far more letters afterwards and thus need to be the word "add". The word “addict” is while in the BIP39 wordlist but you might have made use of “addi” https://bookmarkingace.com/story18800046/top-guidelines-of-bip39-word-list-pdf