For words that only have three letters, there is absolutely no 4th letter. Such as with the word “increase”, there isn't any much more letters afterwards and therefore need to be the word "add". The word “addict” is within the BIP39 wordlist however you might have utilised “addi” for “addict”. https://bookmarkerz.com/story19503049/the-ultimate-guide-to-bip39-seed-phrase-mnemonics-generator