Mythology of Middle Earth

[Keneldil the Polka-dot]

At the risk of sounding stupid...but didn't the writers of ancient mythology actually believe in what they were writing about? JRRT's work doesn't fit in my mind as true mythology because it never was intended to be believed as anything more than just a story.

From Merriam-Webster:

myth
Pronunciation: 'mith
Function: noun
Etymology: Greek mythos
Date: 1830
1 a : a usually traditional story of ostensibly historical events that serves to unfold part of the world view of a people or explain a practice, belief, or natural phenomenon b : PARABLE, ALLEGORY
2 a : a popular belief or tradition that has grown up around something or someone; especially : one embodying the ideals and institutions of a society or segment of society <seduced by the American myth of individualism

Tolkien's stories don't seem to fit any of those definitions of the word 'myth'.