In a manner that is bulbous; in a way that is large, round, and swollen.
From the adjective 'bulbous' plus the adverbial suffix '-ly' from Old English 'lice' (like, in the manner of), forming an adverb.
Adverbs ending in '-ously' are rarer in English descriptive writing, which makes 'bulbously' feel almost comically specific—it appears mostly in botanical descriptions and occasionally in humorous character descriptions.
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