For words that only have 3 letters, there's no 4th letter. As an example with the word “increase”, there isn't any much more letters afterwards and so need to be the word "add". The word “addict” is during the BIP39 wordlist however you would have used “addi” for “addict”. Retail https://worldlistpro.com/story20819256/the-fact-about-bip39-seed-phrase-word-list-that-no-one-is-suggesting