For words that have only three letters, there isn't any 4th letter. Such as with the word “insert”, there won't be any far more letters afterwards and so have to be the word "increase". The word “addict” is during the BIP39 wordlist however, you might have utilized “addi” for “addict”. https://bookmarklayer.com/story19047687/the-definitive-guide-to-bip39-seed-phrase