To buy means to get something by paying money for it. When you buy a book at the store, you exchange your dollars for ownership of that book. Your parents might buy groceries every week, trading money for food and household supplies. The past tense of buy is bought.

The word also describes believing something is true or accepting an idea. If your friend tells you an unlikely story about why their homework is late, you might say, “I don't buy that excuse.” When a teacher buys into a new teaching method, she believes it will work and commits to trying it.

In business, companies might buy other companies to grow larger or gain new capabilities. When someone talks about getting a good buy, they mean they got something valuable for less money than expected, like finding a quality bicycle on sale.

The opposite of buy is sell. In any purchase, one person buys while another sells.