To strengthen is to make something stronger! Rarr. You can strengthen your muscles by working out, or strengthen your brain by learning new words.
Anytime you strengthen something, you're making it more resistant, vigorous, or tough. Taking vitamins can strengthen your immune system so you don't get sick. Lifting weights will strengthen your muscles. A powerful lock will strengthen a door. On computers, a reliable firewall will strengthen your virus protection. If something is weak, it needs to be strengthened. Congrats! You just strengthened your vocabulary by checking out this definition!