Definition: A rhombus is a parallelogram with four congruent sides. *Rhombus I have all of the properties of the parallelogram PLUS - 4 congruent sides-diagonals bisect angles-diagonals perpendicular Using the definition, the properties of the rhombus can be proven true and become theorems. rectangle is a parallelogram with four right angles. While the definition states parallelogram, it is sufficient to say: A quadrilateral is a rectangle if and only if it has four right angles., since any quadrilateral with four right angles is a parallelogram. 2.