An ugly woman serves as a foil to a pretty girl.

一个丑女人可以将美丽的姑娘反衬得更加漂亮。

《新英汉大辞典》

He thought of her serenity as a foil for his intemperance.

在他看来，她的平静反衬出了他的放纵。

youdao

If there are no unhappy as a foil, it would seem plain fun.

如果没有不快乐作陪衬，则快乐会显得平淡。

youdao

So you can imagine, we actually don't need to think of it as a piece of gold foil it might be easier to think of it as a couple of layers of atoms.

所以可以想象,我们不用把它当成一片金箔,只要把它当成是几层原子,所以他所作的就是。

麻省理工公开课 - 化学原理课程节选

Republicans have to figure out -- and fast -- whether they see Hispanics as a foil or as their future.

CNN: GOP's problem with Latinos -- as big as Texas

For years, it has maintained links with Advanced Micro Devices as a foil against the dominance of Intel in microprocessor supply.

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Yet the commitments, for all their weakness, serve a crucial function: They prevent each side from using the other as a foil to justify inaction.

NEWYORKER: Green Giant