In a way that is sweet, pleasant, or charming but becomes tiresome or disgusting because of excess.
From 'cloying' (present participle of cloy) plus the adverbial suffix '-ly,' which converts adjectives into adverbs describing manner or degree.
A song can be cloyingly sweet, or a character can behave cloyingly nice—it's that uncanny valley of sweetness that should be good but feels wrong, like artificial sweetness that's just a little too strong.
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