For words that have only three letters, there's no 4th letter. As an example with the word “increase”, there are no additional letters Later on and therefore need to be the word "increase". The word “addict” is inside the BIP39 wordlist however you would've used “addi” for “addict”. You might https://sirketlist.com/story20350742/facts-about-bip39-seed-phrase-word-list-revealed