in a way that is obvious, conspicuous, or shining brightly; unmistakably.
From 'glaring' (present participle of 'glare') plus the adverb suffix '-ly.' Ultimately from Old Norse 'glarra' (to gleam).
When something is 'glaringly obvious,' it's so obvious that only someone being deliberately blind could miss it—like a neon sign blinking in your face!
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