For words that only have 3 letters, there is not any 4th letter. One example is with the word “include”, there are no more letters Later on and thus must be the word "incorporate". The word “addict” is within the BIP39 wordlist but you would've utilised “addi” for “addict”. BIP39 https://bookmarksknot.com/story21324011/top-latest-five-bip39-seed-phrase-mnemonics-generator-urban-news