means The branch of physics that studies how heat, energy, and work move and transform, governed by a handful of strict laws about energy and entropy.

from A 19th-century scientific compound stitched from Greek thermē, 'heat' (the same root warming thermometer and thermal), and dynamis, 'power' or 'force' (a cousin of dynamic and dynamite). The word was forged as engineers and physicists tried to understand steam engines — literally the science of heat-in-motion — before it grew into the law that governs the fate of stars.