For words that have only 3 letters, there is no 4th letter. By way of example with the word “include”, there won't be any more letters afterwards and therefore must be the word "incorporate". The word “addict” is inside the BIP39 wordlist however, you would've employed “addi” for “addict”. In https://admiralbookmarks.com/story18829500/top-latest-five-bip39-words-urban-news