This is in the strictest confidence.

这事切勿外传。

《牛津词典》

We must practise the strictest frugality and economy.

我们必须奉行最严格意义上的俭朴和节约。

《柯林斯英汉双解大词典》

It's not quite peace in the strictest sense of the word, rather the absence of war.

这个词就其最确切的意义而言不完全是和平，更像是没有战争。

《柯林斯英汉双解大词典》

The government says it is has introduced some of the world's strictest export controls.

BBC: UK arms pledge 'abandoned'

"The second movement is one of the strictest he ever wrote, " Mr. Goode says.

WSJ: Plumbing the Depths of Beethoven | Richard Goode | Cultural Conversation by Stuart Isacoff

"Our gun law is one of the strictest in the whole world, " Mr Stiel says.

BBC: Shootings shock German gun clubs