Quad, Quint, Dec, Cent, Oct

3. An athletic event taking place over two days, consisting of ten different track-and-field events.
7. A geometric shape with eight sides and eight angles.
8. A scale of temperature on which water freezes at 0° and boils at 100° (also known as Celsius).
10. One of four equal parts of something; a coin worth 25 cents.
12. Representing the most perfect or typical example of something.
15. A system of numbers based on the number ten; a fraction whose denominator is a power of ten.
16. A group of five musicians or singers; any set of five.
17. A period of one hundred years.
18. To multiply by four; consisting of four parts.
19. A rate, number, or amount in each hundred.
20. The most perfect or typical example of a quality or class (originally the "fifth element" in ancient philosophy).

1. A group of eight people or things, typically musicians.
2. The two-hundredth anniversary of a significant event.
3. A period of ten years.
4. A series of eight notes occupying the interval between two notes, one having twice the frequency of the other.
5. Four offspring born at one birth.
6. A metric unit of length equal to one-hundredth of a meter.
8. Relating to a hundredth anniversary; a celebration of 100 years.
9. A group of four people playing music or singing together.
11. Historically, to kill one in every ten; in modern usage, to destroy or kill a large percentage of something.
12. An animal that has four feet (e.g., a horse or a dog).
13. A four-sided enclosure, usually a square or rectangular courtyard surrounded by buildings.
14. Five offspring born at one birth.
19. A polygon with five sides and five angles.