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-therm

Also ‑thermal, ‑thermy, ‑thermic, and ‑thermia.

Temperature; heat.

Greek thermē, heat.

Most terms in ‑therm categorise animals on the basis of the way they adapt to changes in ambient temperature: an ectotherm (Greek ektos, outside) is dependent on external sources of body heat; an endotherm (Greek endon, within) is capable of internal generation of heat; a poikilotherm (Greek poikilos, variegated, varied), cannot regulate its body temperature except by its behaviour, such as basking or burrowing. A term with a separate sense is isotherm (Greek isos, equal), a line on a map connecting points having the same temperature at a given time.

Such nouns often have related adjectives in ‑thermal: endothermal, isothermal. Other examples are found in geology, based on the adjective thermal: geothermal, produced by the internal heat of the earth; hydrothermal, denoting the action of heated water in the earth's crust. Some adjectives are formed using ‑thermic: homeothermic, poikilothermic. Exothermic and endothermic have specific senses in chemistry for reactions that are accompanied respectively by the release or absorption of heat.

Nouns in ‑thermy are usually abstract terms for the state: ectothermy, poikilothermy, except that diathermy (Greek dia, through) is a medical technique involving the production of heat in the body by high-frequency electric currents. Some nouns have the ending ‑thermia, for medical states linked to temperature: hyperthermia (Greek huper, over, beyond), the condition of having a body temperature greatly above normal; hypothermia (Greek hupo, under), the reverse condition, of having an abnormally (typically dangerously) low body temperature.

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