As nouns the difference between rival and associate
is that
rival is a competitor (person, team, company, etc) with the same goal as another, or striving to attain the same thing defeating a rival may be a primary or necessary goal of a competitor while
associate is (slang) an associate's degree.
As an adjective rival
is having the same pretensions or claims; standing in competition for superiority.
As a verb rival
is to oppose or compete with.