Thermotropic

Part of speech: adjective

Definitions

1. Describing a material whose optical or physical properties change in response to variations in temperature, such as certain liquid crystals
2. Responding to heat by altering its structure or appearance, as some substances do when they are warmed or cooled
3. Undergoing a reversible change of state or transparency when the surrounding temperature rises or falls

Etymology: Thermotropic is a compound built from two Greek elements. The first, "thermo-", comes from Ancient Greek "thermós", meaning "warm" or "hot", which is also the source of "thermometer" and "thermos". The second, "-tropic", comes from "tropikós", an adjective formed from "trépō", "to turn". So the word literally means "turning toward heat", though in modern use it describes a substance that changes its physical properties, such as its colour, shape or state, in response to temperature. The "-tropic" element is a productive combining form in English. It appears in words like "heliotropic", where plants turn toward the sun, and "phototropic", where organisms respond to light. "Thermotropic" follows the same pattern, applying the idea of directed turning to heat. English speakers formed it by joining the two Greek parts, so the word is a technical coinage rather than something inherited from classical usage.