The Collaborative International Dictionary of English v.0.48:

Intermediary \In`ter*me"di*a*ry\, n.; pl. Intermediaries.
   One who, or that which, is intermediate; an interagent; a
   go-between; a mediator.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Intermediary \In`ter*me"di*a*ry\, a. [Cf. F. interm['e]diaire.]
   Lying, coming, or done, between; intermediate; as, an
   intermediary project.
   [1913 Webster]

   Intermediary amputation (Surg.), an amputation for injury,
      performed after inflammation has set in.
      [1913 Webster]

WordNet (r) 3.0 (2006):

intermediary
    n 1: a negotiator who acts as a link between parties [syn:
         mediator, go-between, intermediator, intermediary,
         intercessor]