For words that have only three letters, there is not any 4th letter. One example is with the word “incorporate”, there won't be any more letters Later on and therefore needs to be the word "increase". The word “addict” is in the BIP39 wordlist however you might have applied “addi” https://madesocials.com/story5091332/facts-about-bip39-seed-phrase-word-list-revealed