(noun) An act of exchanging or trading. Example: "All in all, it was an even exchange."
"The cost of a thing is the amount of what I will call life which is required to be exchanged for it, immediately or in the long run."
"If you have an apple and I have an apple and we exchange these apples then you and I will still each have one apple."
"My solitude doesn’t depend on the presence or absence of people; on the contrary, I hate who steals my solitude without, in exchange, offering me true company."