parliamentarian

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

• noun One who is expert in parliamentary procedures, rules, or debate.
• noun A member of a parliament.
• noun A supporter of the Long Parliament during the English Civil War and the Commonwealth; a Roundhead.

from The Century Dictionary.

• Of or pertaining to a parliament; specifically [capitalized], in English history, serving or adhering to the Long Parliament, in opposition to Kings Charles I. and Charles II.
• noun A partizan of parliament; specifically [capitalized], in English history, a partizan of the Long Parliament, as distinguished from a Royalist or Cavalier.
• noun A parliamentary debater or manager.

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

• noun (Eng. Hist.) One who adhered to the Parliament, in opposition to King Charles I.
• noun One versed in the rules and usages of Parliament or similar deliberative assemblies.
• adjective Of or pertaining to Parliament.

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

• noun A member of a parliament, congress or an elected national legislative body of another name.
• noun A person well-versed in parliamentary procedure.
• noun An officer in most legislative bodies charged with being well-versed in the parliamentary rules of that legislative house, and whose rulings are taken as authoritative, to be appealed only to the whole of the house itself under special rules.

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

• noun an elected member of the British Parliament: a member of the House of Commons
• noun an expert in parliamentary rules and procedures