heater

A "heater" most often means something that makes a place warm, like a space heater, a car heater, or part of a home heating system. In some slang, especially in American English, it can also mean a gun. In baseball, it can mean a very fast pitch, especially a fastball.

So the meaning depends on the situation. If someone says the heater broke in winter, they are probably talking about heat in a room or a car. If a sports announcer says a pitcher is throwing heaters, they mean fast pitches. If it appears in crime stories or slang, it may mean a weapon.

The word "heater" usually brings to mind something that gives off heat. In everyday life, this is the most common meaning. It can be a small electric unit in a room, the system that warms a house, or the part of a car that blows warm air inside. In a sentence like "The heater stopped working," most people will think of this meaning first.

But the word also has other uses. In American slang, "heater" can mean a gun, especially a handgun. You are more likely to see this in movies, novels, song lyrics, or informal speech than in careful formal writing. If someone says a person is "carrying a heater," they mean that person is armed.

There is also a sports meaning. In baseball, a "heater" is a very fast pitch, usually a fastball. An announcer might say that a pitcher is "throwing nothing but heaters" when the ball is coming in with a lot of speed.

So this word moves between everyday life, slang, and sports. One moment it is about staying warm, another moment it is about a weapon, and in baseball it is about speed. The context tells you which meaning is intended.