Is there a term for the phenomenon when you can replace one word in a sentence with a typically opposing meaning word and maintain the meaning of the sentence?
I'm down for that!
I'm up for that!
Admittedly, "fat chance" probably originated as a sarcastic derivation of "slim chance", but in practice, they convey the same thing.
This is slightly related to this question, but that one's asking about a specific case (which may or may not fall into the phenomenon I'm asking about). I'm just looking to see if there is an established term I can use to search for more examples.