In a beefy manner; with muscular strength or solid substance; in a complaining manner.
From 'beefy' + adverbial suffix '-ly'; 20th-century formation describing action performed with beef-like qualities.
Adverbs formed from slang often sound awkward, which is why 'beefily' is rarely used compared to 'beefier'—English speakers find it easier to use adjectives than adverbs for informal descriptive language.
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