For words that only have 3 letters, there is no 4th letter. Such as with the word “increase”, there won't be any additional letters afterwards and therefore need to be the word "include". The word “addict” is within the BIP39 wordlist but you would've applied “addi” for “addict”. This information https://thebookmarkfree.com/story19595718/the-definitive-guide-to-bip39-seed-phrase