An opener is something that opens another thing, or something that begins an event or performance.

The most common use refers to a tool that opens containers. A can opener cuts through the metal lid of a soup can. A bottle opener pops the cap off a glass bottle. Before these inventions, people struggled to get into sealed containers: they sometimes had to cut or smash cans open using whatever tools they had. Each type of opener solves a specific problem, designed for exactly the kind of seal it needs to break.

An opener can also be the first act in a show or the first game in a series. The opening act (or just “the opener”) warms up the crowd before the main performer appears. In baseball, the season opener is the first game of the year, and an opening pitcher starts the game on the mound.

When someone uses a phrase like “for openers,” they mean “to start with” or “first of all.” If you say, “For openers, we need to clean this mess,” you're announcing the first step of a plan. An eye-opener is something surprising that makes you see things differently, like learning an unexpected fact about history that changes how you understand it.