For words that have only three letters, there is not any 4th letter. Such as with the word “increase”, there aren't any additional letters afterwards and therefore have to be the word "add". The word “addict” is in the BIP39 wordlist however , you might have utilised “addi” for “addict”. https://bookmarkspiral.com/story19018326/bip39-seed-phrase-mnemonics-generator-an-overview