Bip39 Vs. The only real explanation those letters are listed is to make it a lot easier for our human brains to go through them And maybe memorize our recovery phrase. The tool will recommend several options for the missing word and also the related one will probably be "asset", https://financenews04603.wikiworldstock.com/1110702/the_anatomy_of_a_bip39_phrase_entropy_phrases_and_security