When we talk about the word "opposite," it means something that is completely different or the exact opposite of something else. Like if you were playing a game of checkers and one player was using the black squares, then the opposite color would be the red squares.
Opposite means that something cannot be more different. It's like saying "no" when someone asks you for something, that's the opposite of saying "yes". Or, another example - if something is really tall, the opposite would be really short.
In summary, opposite means things that are different in the exact opposite way. It's like having a mirror image of something, but everything is switched around.