• (n.) The state or quality of being irreversible; irreversibleness.
(from the article `colloid`) Colloids are generally classified into two systems, reversible and irreversible. In a reversible system the products of a physical or chemical ... ...though they would not violate the fundamental law of conservation of energy. For example, a block of ice placed on a hot stove surely melts, while ... ...in...
Ir`re·vers`i·bil'i·ty noun The state or quality of being irreversible; irreversibleness. 
[n] - the quality of being irreversible (once done it cannot be changed)
noun the quality of being irreversible (once done it cannot be changed)
The inability to mentally reverse an operation.