Real Dictionary

buy
verb: If you buy something, you obtain it by paying money for it.
verb: If you talk about the quantity or standard of goods an amount of money buys, you are referring to the price of the goods or the value of the money.

buy in American English
to get by paying or agreeing to pay money or some equivalent; purchase
intransitive verb: to be or become a purchaser
transitive verb: to acquire the possession of, or the right to, by paying or promising to pay an equivalent, esp. in money; purchase

buy in British English
verb: to acquire by paying or promising to pay a sum of money or the equivalent; purchase