Based on your responses I think one could argue that
1(not a prime) is an opposite of 3(a prime) via your definition of opposite
Time has at least 3 opposites (Length, Width and Depth). By using 2D X=Y lines. (1,0 is the opposite of i,0 is the opposite of 0,1 is the opposite of 0,i)
If I have a set with 1 member, what is the opposite of that member?