1. To buoy, bolster, and help maintain one's spirits or vitalities in difficult or trying situations or periods of time. Your spouse must be someone who lifts you even higher during the best of times and who can sustain you in the worst of times. My sister has always sustained me in situations where it felt like I was completely alone.

2. To provide the necessities, especially nourishment or finances, in difficult or trying situations or periods of time. We have always been able to rely on this brand to sustain us in periods when our other products' sales have been slow. Our mother had to work three different jobs to sustain us in the years after our father left.

3. To provide financial support or stability to one during the course of some task, activity, or endeavor. The board of directors has made it clear that they will sustain us in our new project. Our charity depends on your donations to sustain us in our goal of providing high-quality medical treatments to people in disadvantaged areas.