knee
The knee is a part of the leg. It’s between your thigh and your shin. It’s the joint that allows you to bend your leg. It has a knee cap which protects the joint.
A knee looks like this: 
| get on one’s knees A person gets on his knees when he goes to the ground. |  |
|---|---|
| A doctor checks your knees when you go in for an examination. |  |
| Knee pads help protect your knees.She’s wearing knee pads. |  |
| When a man proposes marriage, sometimes he gets down on one knee. (This is a custom.) |  |
| He got down on his knees to get some water from the river. |  |
| Some people get down on their knees when they pray to God. |  |
| A person who is “weak-kneed” is nervous or weak, or that person lacks courage. |  |