For words that have only three letters, there is absolutely no 4th letter. As an example with the word “include”, there won't be any far more letters Later on and therefore must be the word "incorporate". The word “addict” is in the BIP39 wordlist but you would have used “addi” https://bookmark-group.com/story4368009/an-unbiased-view-of-bip39-seed-phrase-github