Vocabulary: shape

• a shape with four equal sides and four right angles

  Draw a square.

In American geometry, a trapezoid has at least one pair of parallel sides, though some textbooks require exactly one pair. In British English, this shape is usually called a trapezium.

• a quadrilateral with at least one pair of parallel sides

  The students divided the irregular figure into triangles and trapezoids.

Also called a "diamond" in everyday speech. Plural: rhombuses or rhombi.

• a four-sided shape with all sides equal in length but no right angles (unless it is a square)

  A diamond playing-card symbol is shaped like a rhombus.