Word Origin & History. epicene mid-15c., originally a grammatical term for nouns that may denote either gender, from L. epicoenus common, from Gk. Extended sense of characteristic of both sexes first recorded in English c.1600; that of effeminate 1630s.
A parallelogram is a quadrilateral with two pairs of parallel sides. Equivalent conditions are that opposite sides are of equal length; that opposite angles are equal; or that the diagonals bisect each other. Parallelograms also include the square, rectangle, rhombus and rhomboid. Rectangle: all four angles are right angles. 2  An equivalent condition is that the diagonals bisect each other and are equal in length. 3  Informally: a box or oblong (including a square). 4  Square (regular quadrilateral): all four sides are of equal length (equilateral), and all four angles are right angles.
Some parallelograms, such as rectangles and squares, contain right angles. Another type of parallelogram, known as a rhombus, may or may not contain right angles. Quadrilaterals are closed, co-planar geometric shapes that comprise two diagonals and four sides, where all four interior angles have a sum of 360 degrees. Special types of quadrilaterals include parallelograms, rectangles, squares, rhombuses, trapezoids and kites. Parallelograms contain two pairs of opposing sides that are parallel and equally long. The opposite angles of parallelograms are also equal. Rectangles, squares and rhombuses are considered parallelograms because they share the same properties as a parallelogram. The four interior angles of rectangles and squares are all right angles, or 90-degree angles. The opposite angles, also called supplementary angles, have a sum of 180 degrees.