In a way that causes shame, dishonor, or loss of reputation; shamefully or outrageously.
From disgraceful (adjective) + -ly (adverb-forming suffix). Disgrace comes from Old French disgrace, dis- + grace (Latin gratia, favor). The -ly suffix comes from Old English -lic.
Adding '-ly' to 'disgraceful' makes an adverb, but 'disgracefully' sounds sharper than 'shamefully'—the added syllables somehow make the bad behavior sound more deliberate and intentional.
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