What are the differences between an "opposite" and "antonym"?
For all practical purposes, the two are equivalent when used to describe words*.
Etymologically, "opposite" came to us from Latin, via French, while "antonym" came from Greek, also via French.
*as mentioned in my comment below, if the context is not limited to the description of words, then an antonym is a very specific type of opposite -- an opposite of another word.
As of now Wikipedia is considering both the same.
That is, if you search there for
But then again, at the top of the article, Wikipedia notes that
And if you go to the talk page, you will get plenty of reasons why Antonym should never have been moved to Opposite (semantics)
And that article argues that
A good excerpt will be
North is the opposite, but not the antonym, of south.
Antonym means word with opposite meaning".
Opposite and antonym are not synonymous.
In what context?
Opposing is to be against something. The anti-thesis, an enemy of something. Rust is opposite of steel.
Antonym is just a word that is opposite of another.