Cause is what makes something happen. When you flip a light switch, that action causes the light to turn on. When rain falls for days, it causes the river to rise. The cause is the reason behind an effect.

Understanding cause helps us make sense of the world. If your house plants are wilting, you look for the cause: did you forget to water them? Are they getting too much sun? Scientists spend their careers investigating causes: what causes earthquakes, what causes certain diseases, what causes stars to explode. Finding the true cause of a problem is often the first step toward solving it.

The word also means a goal or principle you believe in strongly enough to work for. The abolition of slavery was a cause that Abraham Lincoln devoted his presidency to. Someone might dedicate their life to the cause of education, or raise money for the cause of cancer research. When people say they're fighting for a cause, they mean something bigger than themselves, something they consider worth their effort and sacrifice.

Sometimes people confuse cause with because, but they work differently. You say “the storm caused the power outage” or “the power went out because of the storm,” not “the power went out 'cause of the storm.”