To sustain means to keep something going over time, to maintain it, or to support it so it doesn't fail or fall apart. When a singer sustains a long, clear note, she holds it steady without letting it waver or fade. When a forest sustains a diverse population of animals, it provides enough food, water, and shelter for them to survive year after year.

The word suggests continuous, ongoing support rather than a single moment. A bridge must sustain the weight of traffic day after day. A good breakfast sustains your energy through the morning. A compelling story sustains your interest from the first page to the last. When scientists talk about sustainable practices, they mean ways of doing things that can continue indefinitely without running out of resources or causing damage.

You might hear someone say a basketball team couldn't sustain its early lead, meaning it couldn't maintain its advantage throughout the game. Or a lawyer might say the judge sustained an objection, meaning the judge agreed with it.

In serious contexts, sustain can mean to suffer or endure something difficult: a hiker might sustain an injury on a trail. But the core idea remains: something continues despite challenges or over time.