What does the prefix thermo- mean?
Thermo- comes from the Greek therme, which means "heat". It shows a relation to heat or temperature. It is the prefix of heat in the sciences, and it is used before roots that start with a consonant.
ESEN
Prefix · heat / temperature
thermo-
Signals relation to heat or temperature: thermometer, thermostat, thermodynamics, thermal.
Scientific
Written by Bryan López, English teacher · Updated
Thermo- in technology and geology
Thermo- appears in many fields. In technology, it names devices that measure or regulate temperature and materials that react to heat. In physics, it talks about reactions with extreme heat, like those in the sun. In the atmosphere, it names one of its hot layers. And in geology, it combines with geo- to talk about the Earth's internal heat.
How it is used
Attaches to scientific and technical nouns:
- thermo- + instrument/devicemeter → thermometerstat → thermostatcouple → thermocoupleflask → thermoflask
- thermo- + field/processdynamics → thermodynamicsnuclear → thermonuclearplastic → thermoplasticsphere → thermosphere
The spelling difference is purely orthographic; the meaning is the same.
How it is pronounced
thermo-/ˈθɜːrməʊ/
Tap the button to hear how the prefix sounds. Each word in the table has its own audio.
Examples
Root word
With thermo-
In a phrase
- meterthermometerThe nurse used a digital thermometer to confirm the patient's fever.
- statthermostatSet the thermostat to eighteen degrees to keep the room comfortable.
- dynamicsthermodynamicsThermodynamics studies how heat and energy transfer between systems.
- nuclearthermonuclearStars generate energy through thermonuclear fusion of hydrogen atoms.
- plasticthermoplasticThermoplastic materials can be reshaped by heating multiple times.
- althermalThermal imaging cameras detect heat even in total darkness.
- spherethermosphereThe thermosphere is the outermost atmospheric layer, with extreme temperatures.
Common mistakes
thermometer and thermostat do the same thing
thermometer = only measures temperature; thermostat = measures AND regulates temperature automatically
"Thermometer" only measures (it observes). "Thermostat" measures AND acts: it switches heating or cooling systems on and off automatically when the temperature crosses a set threshold.
thermal = only hot spring water (spa sense)
thermal = relating to heat in any context: thermal energy, thermal imaging, thermal underwear
"Thermal" is a broad adjective meaning "relating to heat": thermal energy, thermal imaging (infrared cameras), thermal underwear (retains body heat), thermal baths (hot spring water). It is not limited to spa contexts.
A trick to remember it
Think of a thermometer, which measures heat: thermo- = heat. thermometer, thermostat.
Practise what you learned
Exercise 1 · Form the word
Exercise 2 · Pick the right one
"Adjust the ___ to eighteen degrees and the system will maintain that temperature automatically."
Exercise 3 · Pick the right one
What is the difference between "thermometer" and "thermostat"?
Frequently asked questions
What does the prefix thermo- mean in English?
The prefix thermo- signals relation to heat or temperature: thermometer, thermostat, thermodynamics, thermal.
How do you pronounce thermo-?
The prefix thermo- is pronounced /ˈθɜːrməʊ/. For example, "thermometer".
Can you give an example of a word with thermo-?
"meter" becomes "thermometer". It is a typical example of the thermo- prefix.
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