Quad (noun)

1. A quadriceps muscle, the large muscle at the front of the thigh that is responsible for straightening the leg.
2. A four-wheeled vehicle, such as an all-terrain vehicle (ATV) or a quadricycle.

Origin:

From latin quādruplum, from quattuor ("four") + -plum ("fold").

Examples:

1. He had a sore quad from playing soccer.
2. The quad was a popular way to get around on the farm.
3. The quad is the muscle that gives the thigh its shape.
4. The quad had four big wheels and was used for off-roading.
5. The quad has become a popular way to explore nature.