A union is when separate things join together to form a single, unified whole. When the thirteen American colonies formed a union during the American Revolution, they stopped acting as thirteen separate governments and began working together as one nation. The word captures this idea of coming together: individual parts combining into something stronger and more complete.

In American history, “the Union” specifically refers to the United States itself, especially during the Civil War when some states tried to leave. President Lincoln worked to preserve the Union, believing the states should remain united rather than split apart.

The word also describes organizations that workers form to negotiate together with their employers. A teachers' union or a factory workers' union gives employees more power by speaking with one voice instead of many separate voices. When workers act in union with each other, they can push for better pay, safer conditions, or fairer treatment.

You'll hear union in other contexts too. A marriage is sometimes called a union between two people. In math, the union of two sets combines all elements from both sets. The key idea stays the same: separate things joining to create something unified and, in many cases, more powerful than the parts alone.