For words that have only three letters, there is absolutely no 4th letter. For instance with the word “include”, there isn't any a lot more letters afterwards and therefore should be the word "insert". The word “addict” is from the BIP39 wordlist but you might have used “addi” for “addict”. https://minibookmarking.com/story18962820/how-much-you-need-to-expect-you-ll-pay-for-a-good-bip39-seed-phrase-mnemonics-generator