Arbitrageur

n. one who practices arbitrage, one who practices arbitrage, one who purchases and sells commodities or financial instruments in various markets to profit from unequal prices without risk (Finance)

In economics and finance, arbitrage is the practice of taking advantage of a price differential between two or more markets: a combination of matching deals are struck that capitalize upon the imbalance, the profit being the difference between the market prices. When used by academics, an arbitrage is a transaction that involves no negative cash flow at any probabilistic or temporal state and a positive cash flow in at least one state; in simple terms, a risk-free profit. A person who engages in arbitrage is called an arbitrageur. The term is mainly applied to trading in financial instruments, such as bonds, stocks, derivatives, commodities and currencies.
See more at Wikipedia.org...

Noun
1. someone who engages in arbitrage (who purchases securities in one market for immediate resale in another in the hope of profiting from the price differential)
(synonym) arbitrager, arb
(hypernym) businessman, man of affairs

One who profits from the differences in price when the same, or extremely similar, security, currency, or commodity is traded on two or more markets. The Arbitrageur profits by simultaneously purchasing and selling these securities to take advantage of pricing differentials (spreads) created by market conditions. See: Risk arbitrage, convertible arbitrage, index arbitrage, and international arbitrage.