If a person or an animal is proppy, they cannot walk or run well. The legs look stiff, as if they were sticks holding the body up rather than swinging freely. You hear this most from horse people in Britain: a horse that is a bit proppy is not moving quite right — maybe sore, maybe lame. People use it of humans too, after a fall or when the knees are old, for that stiff, careful walk. Though actually, this is a small word. Many English speakers have never said it. It is informal, and British more than American. It is not “full of props” on a theatre stage, and it is not a cute form of proper. The picture is the prop that holds something up: the body is using the legs like props, not like living legs.

走不穩、步伐僵硬（多半講馬，也會講人）