noun (n)

• a quadrilateral whose opposite sides are both parallel and equal in length(noun.shape)

  Antonym:
  trapezium
  

  source: wordnet30
• A right-lined quadrilateral figure, whose opposite sides are parallel, and consequently equal; -- sometimes restricted in popular usage to a rectangle, or quadrilateral figure which is longer than it is broad, and with right angles.(noun)

  source: webster1913