Tri - three

: an athletic contest that is a long-distance race consisting of three phases (as swimming, bicycling, and running)

: any of a genus (Triceratops) of large herbivorous quadrupedal ceratopsian dinosaurs of the Late Cretaceous with three horns, a bony hood or crest on the neck, and hoofed toes

: a polygon having three sides

: a group or set of three

: a series of three dramas or literary works or sometimes three musical compositions that are closely related and develop a single theme

: a three-legged stand (as for a camera)

: a number equal to 1,000 times one billion

: a 3-pronged spear serving in classical mythology as the attribute of a sea god (such as Neptune)

: a muscle that arises from three heads

: a 3-wheeled vehicle propelled by pedals or a motor