barrator is also spelled barrater. See also barratry, barratrous, barrat.
From Robert Cawdrey's 1604 A Table Alphabeticall :

a contentious person, quarreller, or fighter

From Samuel Johnson's 1755 A Dictionary of the English Language,

n. s. [from barat, old Fr. from which is still retained barateur, a cheat] A wrangler, an encourager of lawsuits.

Will it not reflect as much on thy character, Nic, to turn barrator in thy old days, a stirrer up of quarrels amongst thy neighbors.
                        --- Arbuthnot's History of John Bull

From Webster's New International Dictionary, 1909

[ME. baratour, OF. barateor deceiver, fr. OF. barater, bareter, to deceive, barter. See barterer, v. i.]

  1. One guilty of barratry.
  2. A fighter; a quarrelsome person; bully; rowdy. Obs.

From : one who engages in barratry