The term PREFIX WITH ANGLE OR ATHLETE can be solved by the THREE-letter word TRI. The prefix TRI is derived from the Greek language and means 'THREE'. It is commonly used in mathematics, science, and other fields to refer to a group of THREE. In terms of angles, it is used to describe a triangle, which is a THREE-sided shape. In terms of athletes, it is used to refer to a triathlete, which is an athlete who competes in THREE different sports.