For words that only have 3 letters, there isn't any 4th letter. Such as with the word “increase”, there isn't any more letters afterwards and thus needs to be the word "incorporate". The word “addict” is within the BIP39 wordlist but you would've utilized “addi” for “addict”. Mnemonic words illustrations https://yesbookmarks.com/story19568908/facts-about-bip39-seed-phrase-word-list-revealed