Circle, circle

I have 1 curved side

Circle, I have no corners.

Triangle, triangle

I have 3 sides

Triangle, I have 3 corners.

Square, square

I have 4 sides

Square, I have 4 corners.

Rectangle, rectangle

I have 2 opposite equal sides

Rectangle, I have 4 corners.

Pentagon, pentagon

I have 5 sides

Pentagon, I have 5 corners.

Hexagon, hexagon

I have 6 sides

Hexagon, I have 6 corners.

Heptangon, heptagon

I have 7 sides

Heptagon, I have 7 corners

Octagon, octagon

I have 8 sides

Octagon, I have 8 corners.