For words that only have 3 letters, there is not any 4th letter. Such as with the word “insert”, there aren't any more letters afterwards and so have to be the word "increase". The word “addict” is inside the BIP39 wordlist however , you would have utilised “addi” for “addict”. https://mysocialport.com/story4283326/top-latest-five-bip39-seed-phrase-mnemonics-generator-urban-news