In a manner characteristic of barking; with a sound or quality resembling a bark.
From 'barking' (present participle of bark) plus the adverbial suffix '-ly.' The double suffix creates an adverb from a gerund or adjective form.
Some adverbs feel forced in English, and 'barkingly' is a prime example—you'd never hear someone say 'she laughed barkingly,' yet the word is theoretically grammatical. It reveals the gap between what English *can* do and what it *does* do.
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