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]

Moby Thesaurus II by Grady Ward, 1.0:

148 Moby Thesaurus words for "intermediary":
   Charlie McCarthy, agency, agent, agential, agentival, agentive,
   amidships, ancilla, appliance, arbiter, arbitrational, arbitrative,
   arbitrator, assisting, average, banal, broker, center, central,
   channel, coming between, common, conducive, connection, contact,
   contrivance, core, creature, deputy, device, distributor, dummy,
   dupe, employable, entrepreneur, equatorial, equidistant,
   facilitating, favoring, forwarding, front, front man, go-between,
   going between, halfway, handmaid, handmaiden, handy, helpful,
   implement, instrument, instrumental, instrumentality, interagent,
   interceder, intercessional, intercessor, intercessory,
   intercurrent, interior, interjacent, interlocutory, intermedial,
   intermediate, intermediate agent, intermediator, intermediatory,
   intermedium, internuncio, interpleader, intervener, intervenient,
   intervening, interventional, interventionist, interventor, jobber,
   judge, lever, liaison, link, mean, mechanism, medial, median,
   mediary, mediating, mediative, mediator, mediatorial, mediatory,
   mediocre, mediterranean, medium, mesial, mesne, mezzo, mid, middle,
   middle-of-the-road, middleman, middlemost, middling, midland,
   midmost, midships, midway, midwife, minion, ministerial,
   ministering, ministry, moderate, mouthpiece, negotiant, negotiator,
   negotiatress, negotiatrix, normal, nuclear, ombudsman, ordinary,
   organ, pacificatory, pawn, plaything, promoting, puppet, referee,
   representative, routine, servant, serviceable, slave, spokesman,
   spokeswoman, standard, stooge, subservient, third party, tie, tool,
   toy, umpire, useful, usual, vehicle, wholesaler