I 'd like to know the definition of this idiom "give him a run for his money". Thanks.
Give him hell, compete fiercely against him.
how so?
Try out our live chat room.

We may not win, but we'll try really, really hard, and we'll make sure that it's not easy for him to win.

I see the underlying mental image here as a running race, perhaps between you and me. Let's each bet $100, and try our hardest. I'll give you a (difficult) run for your money, to beat me you'll have to run very fast.

As mentioned earlier, it's a phrase relating to competition.

Best wishes, Clive
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Incho, Marius, Barbara and Clive,