thermometer

American  

[ther-mom-i-ter] / θərˈmɒm ɪ tər /

noun

1. an instrument for measuring temperature, often a sealed glass tube that contains a column of liquid, as mercury, that expands and contracts, or rises and falls, with temperature changes, the temperature being read where the top of the column coincides with a calibrated scale marked on the tube or its frame.

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thermometer British  

/ θəˈmɒmɪtə /

noun

1. an instrument used to measure temperature, esp one in which a thin column of liquid, such as mercury, expands and contracts within a graduated sealed tube See also clinical thermometer gas thermometer resistance thermometer thermocouple pyrometer

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thermometer Scientific  

/ thər-mŏm′ĭ-tər /

1. An instrument used to measure temperature. There are many types of thermometers; the most common consist of a closed, graduated glass tube in which a liquid expands or contracts as the temperature increases or decreases. Other types of thermometers work by detecting changes in the volume or pressure of an enclosed gas or by registering thermoelectric changes in a conductor (such as a thermistor or thermocouple).

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Other Word Forms

• thermometric adjective
• thermometrical adjective
• thermometrically adverb

Etymology

Origin of thermometer

First recorded in 1615–25; thermo- + -meter

Explanation

A thermometer is a tool that measures temperature — how hot or cold something is. Thermometers are used to see if you have a fever or tell you how cold it is outside. Made up of thermo (heat) and meter (measuring device), the meaning of the word thermometer is pretty straightforward. Thermometers measure temperatures in degrees, according to either the Celsius or Fahrenheit system. Meteorologists use thermometers to find out how hot it is or if it's below freezing. Doctors use thermometers to check your body temperature — a very high or low body temperature means you're sick.

Example Sentences

Basically, he wrote a hit piece on the thermometer instead of asking why he had a fever.

From Slate • Apr. 17, 2026

WSJ | Buy Side: This instant-read thermometer deserves a place in your kitchen.

From The Wall Street Journal • Apr. 6, 2026

In Lancaster and Palmdale, the thermometer hit 88 degrees, which set a new record for each city, according to the weather service.

From Los Angeles Times • Mar. 30, 2026

The bundles include clothing for newborns to six-month-olds, blankets, bibs, muslin cloths, a thermometer, a bilingual book and a playmat.

From BBC • Feb. 2, 2026

My mother knew, of course, that as a weekly Sunday guest at our house, Father Mike was fully informed about the thermometer scheme.

From "Middlesex: A Novel" by Jeffrey Eugenides

Related Words

• instrument
• thermostat