Crossword Genius

Sunglasses not first in the underworld (5)

Ross

I believe the answer is:

hades

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'underworld' is the definition.
(Hades can mean the underworld in Greek myth)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for hades that I've seen before include "The nether world, hell" , "Infernal situation" , "A place of some darkness" , "It's classical hell in the shade" , "Home of the souls of the dead" .)

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