For words that have only 3 letters, there is no 4th letter. Such as with the word “incorporate”, there are no far more letters afterwards and so should be the word "increase". The word “addict” is inside the BIP39 wordlist however , you would've applied “addi” for “addict”. This article https://nimmansocial.com/story8694848/bip39-seed-phrase-mnemonics-generator-an-overview