Unendingly obey a power above, a god (6)

I believe the answer is:

apollo

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'a god' is the definition.
(Apollo is a Greek god)

I don't understand the rest of the clue.

(Other definitions for apollo that I've seen before include "Greek (and Roman) god of light, poetry etc" , "Greek sun god and leader of the Muses" , "handsome youth" , "US spacecraft" , "Greek god; large European butterfly" .)

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