For words that only have 3 letters, there is no 4th letter. By way of example with the word “incorporate”, there aren't any extra letters afterwards and thus must be the word "increase". The word “addict” is from the BIP39 wordlist however, you might have employed “addi” for “addict”. Standard https://tripsbookmarks.com/story19516958/considerations-to-know-about-bip39-seed-phrase-generator