Hi,
Can we say that:
good - bad --- these two words are opposites (diametrical opposites) Yes.
BUT
in --- It was a wonderful party vs. It was a lousy party --- 'wonderful' vs. 'lousy' are NOT opposites but they are in opposition?
In other words, do you agree that good-bad; black-white; male-female etc. are OPPOSITES, while if a pair of words cannot be cleary measured as DIAMETRICAL OPPOSITES, it is better to say that they are IN OPPOSITION (rather than they are OPPOSITES)?
The term 'in opposition' may perhaps be commonly used like this in technical linguistic discussions. I don't know. But it is not used like this in everyday English, where the word 'opposition' usually suggests resistance, antagonism. eg There was a lot of opposition to his idea.
Best wishes, Clive