For words that have only 3 letters, there's no 4th letter. For instance with the word “incorporate”, there won't be any more letters Later on and thus needs to be the word "incorporate". The word “addict” is in the BIP39 wordlist however you would've utilized “addi” for “addict”. Mnemonic words https://bookmarkity.com/story18946525/the-fact-about-bip39-seed-phrase-word-list-that-no-one-is-suggesting