Well, "opposites" made me think of the big LBT one. I immediately of sharpteeth and flateeth. I have a few reasons:
The obvious one: the type of teeth they have
One type mostly fights while the other prefers peace
One type fends for themselves at the right age, the other tries to remain in groups
And a few other things, but you should get the idea now of why this flashed in my mind after hearing "opposites." So here is what the next person looks at:
Sharpteeth and Flateeth
I know that this seems like two things but it is really one: the comparison between these two. But this can still be easy with two words. Dinosaurs, teeth, and many other words still come to mind with them so please don't think I left a nearly impossible theme. Later!