Uni, Bi, Tri, Quad

4. A dinosaur with three horns - two long horns above the eyes and one short horn on the nose
6. A horse-like fabled animal that has one horn growing out of the middle of its forehead
10. To create four times as much or as many of something
11. Having two different colors
12. One of a kind; unusual or rare
14. To cut into three parts
16. A vehicle with three wheels
18. A race that combines three activities - swimming, bicycling, and running
20. A plane figure in geometry that has four sides (including square, rectangle, rhombus, parallelogram, and trapezoid)

1. A muscle group consisting of four muscles that is located along the front of the thigh
2. The ability to speak four languages
3. Having only one cell
5. An airplane with two pairs of wings
7. Able to speak two different languages
8. A one-wheeled vehicle on which the rider sits and pedals
9. A four-sided enclosure, usually surrounded by buildings
13. Moving in only one direction
15. A vehicle with two wheels
17. Happening every two months
19. Three related plays or novels