What is a thenometer?

Answer 1

1. ther·mom·e·ter

   noun /THərˈmämitər/ 

   thermometers, plural

   1. An instrument for measuring and indicating temperature, typically one consisting of a narrow, hermetically sealed glass tube marked with graduations and having at one end a bulb containing Mercury or alcohol that expands and contracts in the tube with heating and cooling

Answer 2

It seems like there might be a typo in your question. Did you mean "thermometer"? If so, a thermometer is a tool used to measure temperature. It typically consists of a glass tube filled with a liquid that expands or contracts with temperature changes.