Entropy is a term used in thermodynamics and statistical mechanics to describe the amount of disorder or randomness in a system. It is often referred to as a measure of CHAOS. The term entropy can be broken down into two parts: 'EN' meaning within and 'tropos' meaning change. In other words, entropy is a measure of the amount of energy that is unavailable for work within a system. The crossword solution for entropy is CHAOS, which is an apt description of the concept.