For words that only have 3 letters, there's no 4th letter. For instance with the word “increase”, there aren't any extra letters afterwards and so must be the word "increase". The word “addict” is while in the BIP39 wordlist however , you would've utilized “addi” for “addict”. This post clarifies https://throbsocial.com/story20668973/top-latest-five-bip39-seed-phrase-mnemonics-generator-urban-news