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trivial; trifling; insignificant; not worth bothering with; worthless; useless; good-for-nothing
stupid; nonsensical; absurd; foolish; silly
くだらない冗談を言って場を盛り上げた。
I livened up the atmosphere with silly jokes.
あの映画はくだらなかったが友達は笑っていた。
That movie was worthless, but my friends were laughing.
この本の内容はくだらなくないと思うよ。
I think the content of this book isn't trivial.