In a bright, loud, or excessively showy manner that is unpleasant or offensive to the eye.
From garish (excessively bright or showy) plus -ly (adverb-forming suffix). Garish comes from possibly Germanic origins related to 'gare' (ready, nimble), suggesting something that sticks out obviously.
The word 'garish' might come from an old Germanic root meaning 'ready' or 'nimble'—so something garishly colored literally stands out as 'ready to be noticed'!
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