1. A situation in which two or more people, groups, organisations or businesses are trying to get something which not everyone can have. English = competition, rivalry.
2. Someone you are competing with. English = competitor, rival.
3. In a game or competition, the person who is playing against you; in politics, the political group or party that is not part of the government. English = opponent, opposition; opposition.
4. An illness that you have when you eat, smell, or touch a substance which does not normally make people ill. English = allergy.