Thermodynamics

The third entry is a entropia, and « entropy » is one of the few technical words whose birth is on record. Rudolf Clausius made it in 1865 out of the Greek en, in, and tropḗ, a turning or a transformation, and he said plainly why he had chosen that shape: he wanted a name as close as possible to the sound of « energy », because the two quantities were meant to be thought about together. The word is therefore not a description of anything but a deliberate twin. Its Greek half is not at all rare in English, merely unrecognised. « The tropics » are the latitudes at which the sun turns back; « a heliotrope » is a flower that turns with the light; « a trope » is a figure of speech, a turn given to a word. Knowing this makes the quantity no easier, but it does settle one thing that beginners assume too quickly. The name says nothing whatever about disorder: it names a turning, and disorder is an interpretation laid over it long afterwards.