For words that have only 3 letters, there's no 4th letter. By way of example with the word “increase”, there isn't any far more letters afterwards and therefore need to be the word "increase". The word “addict” is within the BIP39 wordlist however you might have employed “addi” for “addict”. https://socialdosa.com/story8613811/an-unbiased-view-of-bip39-seed-phrase-github