Apposite means appropriate, relevant, or well suited to a situation. It is often used for remarks, examples, or responses that fit especially well. If a comment is perfectly timed and directly relevant, it is apposite.
Opposite usually means across from, facing, or completely different. You can use it for physical position, such as one building being opposite another, or for contrast, such as two ideas having opposite meanings.
The easiest way to separate them is this: if you mean fitting, choose apposite. If you mean across from or contrary, choose opposite.
- Her calm reply was apposite to the tense moment.
- The pharmacy is opposite the library.
- The twins have opposite tastes in music.
These words may look similar, but they are not interchangeable. A remark can be apposite, but not opposite. A building can be opposite another building, but not apposite to it.