For words that have only three letters, there isn't a 4th letter. By way of example with the word “incorporate”, there aren't any more letters afterwards and so have to be the word "include". The word “addict” is inside the BIP39 wordlist but you would've employed “addi” for “addict”. Meticulously https://health-lists.com/story19436412/bip39-seed-phrase-fundamentals-explained