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.
A convex quadrilateral is a square if and only if it is any one of the following: 1  a rectangle with two adjacent equal sides. 2  a rhombus with a right vertex angle. 3  a rhombus with all angles equal. 4  a parallelogram with one right vertex angle and two adjacent equal sides. 5  a quadrilateral with four equal sides and four right angles.