For words that have only 3 letters, there's no 4th letter. Such as with the word “include”, there are no extra letters Later on and therefore has to be the word "increase". The word “addict” is in the BIP39 wordlist however you would have made use of “addi” for “addict”. https://bookmarkahref.com/story19033293/detailed-notes-on-copyright-wallet-seed-phrase-out-of-bip39