For words that only have three letters, there is no 4th letter. By way of example with the word “incorporate”, there won't be any far more letters afterwards and thus have to be the word "include". The word “addict” is in the BIP39 wordlist but you might have utilized “addi” https://bookmarkworm.com/story18985698/the-fact-about-bip39-seed-phrase-word-list-that-no-one-is-suggesting