For words that only have 3 letters, there's no 4th letter. For instance with the word “increase”, there won't be any much more letters Later on and therefore has to be the word "add". The word “addict” is from the BIP39 wordlist but you would have applied “addi” for “addict”. https://seobookmarkpro.com/story18924858/details-fiction-and-bip39