For words that only have three letters, there's no 4th letter. As an example with the word “add”, there won't be any extra letters afterwards and thus needs to be the word "incorporate". The word “addict” is in the BIP39 wordlist however, you might have made use of “addi” for https://socialwebleads.com/story4237679/the-ultimate-guide-to-bip39-seed-phrase-mnemonics-generator