Mythical means belonging to old stories rather than to fact. A mythical creature.
It also means so famous that the truth has been lost, which is the looser everyday use. A mythical reputation is one nobody now checks.
1adjectivemythicalBelonging to old stories rather than to fact.
“Half the mythical creatures on the map were sailors' mistakes.”
mythical is a quality.
Greek mythikos comes from mythos, a story or a word.
Ancient Greek
μῦθος
English
myth
English, today
mythical
From mȳthicus + -al. From mȳthicus + al; by surface analysis, myth + -ical. myth Borrowed from Ancient Greek μῦθος. From Ancient Greek μῦθος (“word, humour, companion, speech, account, rumour, fable”). Attested in English since 1830. a doublet of mythos.
Etymology from Wiktionary, CC BY-SA