a medium of exchange

a Determinative

— A is used when the following word could be any of a certain type. Compare "A book I saw on the shelf" and "The book I gave you yesterday".

a Noun

— A is the first letter of the alphabet. The letter "a" comes before "b". — In some schools, an A is a very high grade. Ron got an A on his earth science test.

medium Adjective

— A medium amount is an amount that is not small and not large, but in the middle. Would you like a small, medium or large drink?

medium Noun

— A medium is stuff that something moves through. Light can go through different media: air, water, glass. Sound waves slow down when they go through this kind of medium. — A medium is a person who hears ideas that come from people who are dead. We all closed our eyes, and the medium said "I hear your father speaking." I don't believe those mediums can really hear anything.

of Preposition

— Made using. It is a house of cards.

exchange Verb

— Two people exchange two things when each person gives a thing to the other person. They can exchange two things, or they can exchange a thing for money. The children can exchange toys so that each child has a new toy to play with.

exchange Noun

— An exchange is the act of exchanging. I did well in that exchange. Now I have three good new books, and I only paid a little money.