切り札

あの会社の社長は切り札を隠し持っています。

The president of that company has an ace up her sleeve.

切り札は最後まで見せるな。見せるなら、さらに奥の手を持て。

Keep that ace up your sleeve. If you're going to show it, have another even further up.

きっと無罪になるだけの決定的切り札を隠し持っているに違いない。

I'm sure he has something up his sleeve.

「背が伸びて入(はいる)らないわよね」「そう、断じて太ったわけではない！」「成長したという便利な言葉は我々の切り札」

"We've got taller so they don't fit." "Right, it's certainly not that we've got fat!" "The useful phrase 'grown up' is our trump card."