Edited for clarity... Opponent is someone who is against/your competitor “My opponent is stronger than me.” Opposed is to be against/not like something or someone “I am opposed to going to the movies.” Opposing is the act “The opposing army has a lot of weapons.” Opposite is similar to across/different depending on context “He sat opposite me on the bus.” Or “I took the opposite position of my friend.” Opposition is like a challenger. “The opposition forces are attempting to overthrow the government.”

Opponent is some who is against your competitor “My opponent is stronger than me” Opposed is to be against/not like something or someone “I am opposed to going to the movies.” Opposing is the act “The opposing army has a lot of weapons.” Opposite is similar to across or different depending on context “He sat opposite eme on the bus.” Or “I took the opposite position of my friend.” Opposition is like a challenger. “The opposition forces are attempting to overthrow the government.”

They occupy different parts of speech. They mean generally the same thing but are used slightly differently depending on where they belong in a sentence. Examples: I am your opponent. You must fight me. I am opposing you. You are opposed to me. I am opposite you (meaning something like "I'm standing in front of you"). You are my opposition in this fighting competition.