Luster is the way light reflects off a surface, giving it a particular kind of shine or glow. A freshly polished silver spoon has a bright, mirror-like luster. A pearl has a soft, glowing luster that seems to come from within. Different materials have different lusters: metals tend to have a brilliant, reflective luster, while silk has a subtle, flowing luster as light plays across its surface.

When something loses its luster, it becomes dull and less attractive. An old penny that's turned dark and tarnished has lost the bright luster it had when new. You might polish your shoes to restore their luster before a special occasion.

The word also describes a quality of excellence or appeal. A once-popular restaurant that has lost its luster might have declining food quality or service. A lackluster performance is one that's disappointing or uninspired, like a soccer team playing without energy or enthusiasm.

When something has luster, whether it's a polished gemstone or a person's reputation, it catches attention and stands out. Scientists and jewelers use specific terms to describe luster precisely, such as metallic luster, pearly luster, or glassy luster.