To strengthen means to make something stronger or more powerful. When you strengthen your muscles by exercising regularly, they grow bigger and can do more work. When a builder strengthens a bridge by adding extra steel beams, the bridge can safely hold more weight.

You can strengthen physical things like walls, ropes, or your grip on a baseball bat. But you can also strengthen things you can't touch. A teacher might strengthen students' understanding of fractions through extra practice. A friendship strengthens when two people spend time together and support each other through difficult situations. A country might strengthen its laws to better protect its citizens, or strengthen its economy by encouraging new businesses.

Notice that strengthening usually takes time and effort. Your reading skills strengthen gradually as you read more challenging books. A team's defense strengthens through hours of practice together. When something strengthens, it becomes more capable, more durable, or better able to handle challenges.