For words that only have three letters, there is absolutely no 4th letter. For instance with the word “insert”, there are no more letters Later on and therefore must be the word "add". The word “addict” is in the BIP39 wordlist however , you might have utilised “addi” for “addict”. https://bookmarklinking.com/story4975223/top-latest-five-bip39-seed-phrase-mnemonics-generator-urban-news