For words that only have 3 letters, there is no 4th letter. By way of example with the word “incorporate”, there isn't any additional letters afterwards and thus must be the word "incorporate". The word “addict” is inside the BIP39 wordlist but you would've utilised “addi” for “addict”. On this https://bbsocialclub.com/story20875569/the-fact-about-bip39-seed-phrase-word-list-that-no-one-is-suggesting