middleman

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A trader who buys from producers and sells to retailers or consumers.
• noun An intermediary; a go-between.

from The Century Dictionary.

• noun One who acts as an intermediary between others in any matter; an intermediate lessee, contractor, negotiator, trader, broker, etc.; specifically, one who buys merchandise in bulk to sell it in smaller quantities to other traders or to retail dealers; in Ireland, a lessee of a tract of land who sublets it in parcels at an advanced rate to actual tenants or occupiers; more generally, any one who acts as a buyer and seller, or undertaker for profit, between producers or principals and consumers, users, or executants.
• noun A man of intermediate rank; a commoner.
• noun In the fisheries, a planter.
• noun In negro minstrelsy, the man who sits in the middle of the semicircle of performers during the opening part of the entertainment, and leads the dialogue between songs.

from the GNU version of the Collaborative International Dictionary of English.

• noun An agent between two parties; a broker; a go-between; any dealer between the producer and the consumer; in Ireland, one who takes land of the proprietors in large tracts, and then rents it out in small portions to the peasantry.
• noun A person of intermediate rank; a commoner.
• noun (Mil.) The man who occupies a central position in a file of soldiers.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An intermediary, agent between two (or more) parties
• noun An intermediate dealer between the manufacturer and the retailer or customer

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a person who is in a position to give you special assistance
• noun someone who buys large quantities of goods and resells to merchants rather than to the ultimate customers
• noun the performer in the middle of a minstrel line who engages the others in talk