noun (n)

• a parallelogram with four equal sides; an oblique-angled equilateral parallelogram(noun.shape)

  Synonym:
  diamond, rhombus
  

  source: wordnet30
• An equilateral parallelogram, or quadrilateral figure whose sides are equal and the opposite sides parallel. The angles may be unequal, two being obtuse and two acute, as in the cut, or the angles may be equal, in which case it is usually called a square.(noun)

  source: webster1913