Difference between "mythical" and "mythological"

• mythological is from an accepted tradition of mythical stories, like the Roman or Hindu or Navaho religions.
• mythical is anything fantastic or imaginary or fictitious.

So 'mythological is a subset of 'mythical'. The myths of the Roman religion make up Roman mythology. They are considered mythical, as are the Easter Bunny or Tooth Fairy. One could say that -any- fiction (like say 'Jane Eyre') is mythical because it is fiction, but there is the need for the idea of the fantastic for 'mythical' to apply.

Chambers has...

mythical adj 1 relating to myth. 2 imaginary; untrue.

mythology noun (mythologies) 1 myths in general. 2 a collection of myths, eg about a specific subject. 3 the study of myth or myths. mythological adj relating or belonging to mythology.

myth noun 1 an ancient story that deals with gods and heroes, especially one used to explain some natural phenomenon. 2 such stories in general; mythology. 3 a commonly-held, false notion. 4 a non-existent, fictitious person or thing.

So mythical is related to a [particular] ancient story. "The Minotaur is a mythical beast."

Mythological is related to a collection of mythical stories or the system of belief they describe. "In Greek Mythology, Hera was the wife of Zeus, the greatest god."