Resembling or characteristic of a guardian; protective and responsible in manner.
From guardian plus the adjectival suffix -ly (note: -ly here creates an adjective, not an adverb, as it historically did). This dual-use suffix shows English's evolution toward clarity in word formation.
English has a tricky quirk: -ly usually makes adverbs ('quickly,' 'slowly'), but it also makes adjectives from nouns ('manly,' 'cowardly,' 'guardianly'), and we don't always distinguish them in speech—a fascinating historical remnant.
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