For words that only have three letters, there isn't any 4th letter. For instance with the word “increase”, there aren't any more letters afterwards and thus needs to be the word "add". The word “addict” is during the BIP39 wordlist but you would've employed “addi” for “addict”. Artwork is usually https://livebookmarking.com/story18809938/facts-about-bip39-seed-phrase-word-list-revealed