meaning of "exercise care"

Question

From a tutorial

“below” and “beneath” can refer to people or things that are unworthy in some way or of a lower social ranking.

...

Some people think she married below her family.

This meaning is negative, however. So exercise care when using it.

Does "exercise care" means here "be careful"? Is it an idiom? I looked it up in some dictionaries but didn't find an item/entry for it.

Should I go with these meanings in the Cambridge Dictionary and put them together?

exercise: to do physical activities to make your body strong and healthy

care: the process of protecting someone or something and providing what that person or thing needs

Answer 1

This is not an idiom, but the definitions you provided are incorrect. It does appear to be a bit difficult to find the appropriate definitions that fit this fairly common phrase. Here are the best I could find.

From Macmillan Dictionary:

Exercise (TRANSITIVE VERB)
to use a skill or personal quality, especially in order to avoid problems
Caution must be exercised when operating this equipment.

Care (UNCOUNTABLE NOUN)
effort and attention
I can see that a lot of care has gone into your work.

So if I use these definitions together, it would be:

To exercise care means to *use effort and attention to avoid problems.

But it can be simplified:

To exercise care means to use caution. So your understanding of be careful is correct.