For words that only have 3 letters, there is no 4th letter. For example with the word “incorporate”, there aren't any more letters Later on and therefore should be the word "add". The word “addict” is in the BIP39 wordlist however you would've utilized “addi” for “addict”. Mnemonic words illustrations https://bookmarkspring.com/story14482510/new-step-by-step-map-for-ledger-seed-phrase-bip39