The Collaborative International Dictionary of English v.0.48:

Rectangle \Rec"tan`gle\ (r?k"t??`g'l), n. [F., fr. L. rectus
   right + angulus angle. See Right, and Angle.] (Geom.)
   A four-sided figure having only right angles; a right-angled
   parallelogram.
   [1913 Webster]

   Note: As the area of a rectangle is expressed by the product
         of its two dimensions, the term rectangle is sometimes
         used for product; as, the rectangle of a and b, that
         is, ab.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rectangle \Rec"tan`gle\, a.
   Rectangular. [R.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

rectangle
    n 1: a parallelogram with four right angles