ἐν + τροπή

Entropy was coined in 1865 by the German physicist Rudolf Clausius from Greek ἐν (en, 'in') and τροπή (tropē, 'transformation, turning, change'), producing a word meaning roughly 'the content of transformation' or 'that which turns.' Clausius was deliberate in his choice of Greek roots: he wanted entropy to parallel 'energy' (from Greek ἐνέργεια, energeia, 'activity, operation'), a word that had been coined a century earlier from Greek en + ergon (work). Energy and entropy were to be companion concepts, both measured in thermodynamic systems, both expressed in Greek. Clausius wrote: 'I have intentionally formed the word entropy so as to be as similar as possible to the word energy; for the two magnitudes to be denoted by these words are so nearly allied in their physical meanings, that a certain similarity in designation appears to be desirable.' The naming was deliberate symmetry.