noun. One who is opposed to monopolies; one who desires to restrict the power and influence of great corporations, as tending to monopoly.

noun. One who opposes monopolies.

"But Vanderbilt's parents passed on a shrewd and merciless business sense — his mother once foreclosed on her own widowed daughter's mortgage — and as a young man he quickly found a mentor in Thomas Gibbons, whose battle against a steamboat rival led to the landmark Supreme Court case Gibbons v. Ogden, which struck a blow for antimonopolist laissez-faire principles."

antimonopolism