Is there any term in English for a situation when two opposite words give the same meaning.

The thick trees on either side of the street deepened its horror.

The thick trees on either side of the street heightened its horror.

It's a slightly different situation.

Twenty people have left. Now only one is left.


The first is an interesting case, though I don't think 'deepened' collocates well there. But I don't know a word for it.

The second case is just a case of verb forms, I think. 20 people have left and one is (has been) left.
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Thanks, MM!

Are these natural collocations?

...deepened its mystery.

...heightened its mystery.


PS: I can't edit my first post now. Could you please correct the spelling mistake? Thick trees...
Heightened sounds natural to me there, too.