For words that have only three letters, there isn't any 4th letter. By way of example with the word “increase”, there aren't any extra letters afterwards and thus need to be the word "insert". The word “addict” is in the BIP39 wordlist however, you would've made use of “addi” for https://loanbookmark.com/story18906575/the-fact-about-bip39-seed-phrase-word-list-that-no-one-is-suggesting