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1. (of light or color) very bright and radiant.

〖通例名詞の前で〗光り輝く, きらきら光る〈日光など〉; 鮮やかな〈色など〉 (!brightより強い輝き)

2. exceptionally clever or talented:

〈人･考え･演技などが〉すばらしい, 見事な; 才能あふれる, 優秀な

e.g. a brilliant young mathematician

e.g. a brilliant idea.

outstanding; impressive:

〈業績･成功などが〉輝かしい, 立派な

e.g. his brilliant career at Harvard.

3. British informal very good, excellent, or marvelous:

｟英話｠ すてきな, 楽しい; 〈人が〉 【人に対して】とても親切な «with»

e.g. we had a brilliant time

e.g. as exclamation : “Brilliant!” he declared excitedly as she finished telling him what had happened.

a diamond of brilliant cut.

ブリリアントカットの宝石, ダイヤモンド

late 17th century: from French brillant ‘shining’, present participle of briller, from Italian brillare, probably from Latin beryllus (see beryl).