To act as a mediator in a dispute; to arbitrate or mediate.
To plead on someone else's behalf.
To pass between; to intervene.
To mediate, to be an intermediate.
To arrange, in the manner of a broker.
Any substance formed as part of a series of chemical reactions that is not the end-product.
An intermediary.
Anything in an intermediate position.
Being between two extremes, or in the middle of a range.