While all these words are similar, here are a few supple difference in usage. The word "competitor" is used in general to describe any person who competes in a contest for a prize or award. The word "rival" suggests a more intense or emotional struggle between individuals. The word "contender" is often reserved for someone who has a real chance to win the top prize! The words "contestant" is used more for those involved in contests that do not involve sport, such as game shows. Hope this helps