Is it dullness?
It’s hard to say because shine could be a noun or a verb.
And I can’t think of an antonym for either. Dullness is more a lack of shine, rather than the opposite.
I suppose when speaking metaphorically, retreat could be the opposite of shine. If something or someone isn’t actively being noticed for its sparkle, one could say it’s retreating.
I’ll be stuck on this all night tonight. I know there’s something profound within or beneath the question.
There’s an opposite to love, right? We can hate something.
But is there an opposite to shining?
How many words don’t have antonyms?
It’s not “dark” because something can be bright, or colorful, even white, and not be shiny.
What an interesting, frustrating, wonderful word.