In a bragging or boastful manner; while bragging or with a tendency to boast.
Formed from the present participle 'bragging' (brag + -ing) plus the adverbial suffix '-ly.' This construction converts the gerund/participle into an adverb describing how an action is performed. The '-ly' suffix is English's primary method for creating adverbs from adjectives and other forms.
The '-ly' adverb suffix is so productive that English speakers can almost always create an adverb from an adjective by adding it—'quickly,' 'happily,' 'braggingly'—even for words speakers rarely use! This explains why you might hear 'unfortunately' in formal speech but never encounter 'bragginglily,' because the pattern works too well.
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