For words that only have 3 letters, there is not any 4th letter. For example with the word “increase”, there won't be any a lot more letters afterwards and therefore should be the word "insert". The word “addict” is from the BIP39 wordlist however you would've utilized “addi” for “addict”. https://bookmarketmaven.com/story19398644/new-step-by-step-map-for-bip39-english-words