what is the instrument used to measure temperature

The instrument used to measure temperature is called a thermometer.

Quick Scoop: What You Asked

You asked: “what is the instrument used to measure temperature”.
In science, physics, and everyday life, the standard name for that instrument is thermometer.

One-line school-style answer

• The instrument used to measure temperature is a thermometer.

A bit more context (still short)

When you place a thermometer in contact with a body or in a room, it responds to how hot or cold it is and shows a value, usually in degrees Celsius (°C), Fahrenheit (°F), or sometimes Kelvin (K). Different types exist (like digital or mercury thermometers), but the general name for any instrument that measures temperature is still “thermometer.” TL;DR: Instrument for measuring temperature = thermometer.