risk arbitrage: arbitrage involving risk; as in the simultaneous purchase of stock in a target company and sale of stock in its potential acquirer; if the takeover fails the arbitrageur may lose a great deal of money
arbitrage: a kind of hedged investment meant to capture slight differences in price; when there is a difference in the price of something on two different markets the arbitrageur simultaneously buys at the lower price and sells at the higher price
speculator: someone who risks losses for the possibility of considerable gains