'garish' originates from Middle English, specifically the (now obsolete) word 'garishen', where the root is uncertain but may have conveyed roughness or harshness.

'garish' changed from the Middle English word 'garishen' and eventually became the modern English adjective 'garish' from which the adverb 'garishly' is formed.

Initially, it likely meant something like 'rough' or 'harsh', but over time it evolved into the current meaning of 'excessively showy or gaudy'.