1. quadrangle

2. a type-metal space that is one en or more in width

3. to fill out (something, such as a typeset line) with blank space

4. quadruplet

5. a ski lift that holds four people

6. a quadruple toe loop in competitive figure skating

7. a four-wheeled all-terrain vehicle

8. having or composed of four items or elements quadruple sense 1
The F/A-18 flight-control system … is characterized by quad redundancy, which means that there are essentially four levels of sensing and actuation for each control surface.
— McGraw-Hill Yearbook Of Science And Technology Quad skates are roller skates that have four wheels arranged in two rows, while inline skates have them in one line.
— Jenee Osterheldt

9. quadraphonic
Domestic quad listening needs two additional loudspeakers over stereo, and two more amplifiers, plus the black box which allocates some of the sounds to the rear left/right, and others to the front left/right.
— George Steedman

10. quadraphonic sound

11. a unit of energy equal to one quadrillion British thermal units

12. the greater extensor muscle of the front of the thigh that is divided into four parts quadriceps —usually plural
"Usually after a heptathlon I can tell if I'm not going to do well jumping. My quads get tired."
— Jackie Joyner-KerseeDick Williams, Seattle manager, on shortstop Spike Owen's injured quads: "I never had any quads when I played."
— Sports Illustrated

13. quadriceps —usually used in plural