An arch is a structure that is curved at the top and is supported on either side by a pillar, post, or wall.

An arch is a curved line or movement.

The arch of your foot is the curved section at the bottom in the middle.

If you arch a part of your body such as your back or if it arches, you bend it so that it forms a curve.

If you arch your eyebrows or if they arch, you move them upwards as a way of showing surprise or disapproval.

If something arches in a particular direction, it makes a curved line or movement.

An arch look is mysterious and mischievous.

If you say that someone is arch, you are criticizing them for talking or behaving as if they are better or more important than other people.