In a manner characterized by caution, protection, or wariness; defensively or cautiously.
From the present participle guarding (guard + -ing) plus the adverbial suffix -ly, creating an adverb that describes the manner of performing an action with protective intent.
The -ing form creates dynamic energy in adverbs—'guardingly' suggests ongoing, active protection rather than static watchfulness, which is why you'll see it in narratives about characters behaving defensively.
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