In a flashing or sudden manner; resembling or characteristic of a flash of light.
Formed by adding '-ly' directly to 'flash' as an adjective base, though 'flashily' is the more standard adverbial form.
The existence of both 'flashly' and 'flashily' shows the messiness of English word formation—both theoretically work, but only 'flashily' is considered standard, showing how languages have many possible forms but conventions narrow them down.
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