superlative
US /səˈpɝː.lə.t̬ɪv/
UK /səˈpɝː.lə.t̬ɪv/

1.
of the highest quality or degree
:
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The chef prepared a superlative meal for the guests.
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Her performance was truly superlative.
1.
the highest degree of comparison of an adjective or adverb (e.g., 'biggest', 'most beautiful')
:
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In grammar, 'tallest' is the superlative form of 'tall'.
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She used the superlative 'most beautiful' to describe the sunset.