Rival
A rival is a person or group of people who are trying to do the same thing as someone else, and trying to do it better. They are "competing" against one another. Usually they are about equally good.
Competing in this way is called rivalry.
Two (or more) businesses may be rivals. For example: they may be selling ice creams in the same area.
Brothers and sisters may be rivals. For example: they may both be trying to get their mother's attention.
Countries may be rivals. For example: they may be trying to have power over the same thing. This can be a dangerous thing which, in some cases, can lead to war.
In sport, two teams may be rivals. This is a more friendly kind of rivalry.
Rival Media
Winston Churchill and Neville Chamberlain were political rivals for the leadership of the UK for much of the 1930s as the Second World War loomed.
The rivalry between Millwall F.C. and West Ham United F.C. is one of the oldest and bitterest in the history of English football.
The rivalry between Celtic F.C. and Rangers F.C., both Glasgow teams, is based on the ethno-political sectarianism of The Troubles.