For words that have only three letters, there isn't any 4th letter. For example with the word “incorporate”, there aren't any extra letters Later on and therefore has to be the word "increase". The word “addict” is inside the BIP39 wordlist however, you would've made use of “addi” for “addict”. https://allkindsofsocial.com/story4804887/how-much-you-need-to-expect-you-ll-pay-for-a-good-bip39-seed-phrase-mnemonics-generator