Bip39 seed words https://www.demilked.com/author/gobnettlmz/ Though it employs BIP32 technique you may however import BIP39 seeds into Electrum wallet. Also aside from BIp32 There exists BIP44 Model which some wallet use for the technology of seeds. For words that only have three letters, there isn't any 4th letter. One example is https://bookmark-master.com/story20523451/bip39-rust-rumored-buzz-on-bip39-generator-https-cutt-ly-uryc5rw7