For words that have only 3 letters, there's no 4th letter. For example with the word “insert”, there won't be any a lot more letters Later on and so must be the word "increase". The word “addict” is from the BIP39 wordlist however, you might have applied “addi” for “addict”. https://kingbookmark.com/story18874179/little-known-facts-about-bip39-words