is a square a trapezoid.
No. In order for a quadrilateral to be a trapezoid, it must have exactly one pair of parallel sides. A right trapezoid, therefore, has exactly one pair of right angles. However a square would be a right parallelogram (which is the current definition of a rectangle). In the UK, the word trapezoid refers to a quadrilateral with no sides parallel. They use the word trapezium to refer to what Canadians call a trapezoid. To make matters worse, North Americans call a quadrilateral with no parallel sides a trapezium. Here's a summary.