What is the meaning of the word "arbitrage"?

Definitions:

a kind of hedged investment meant to capture slight differences in price by simultaneously buying and selling the same commodity on multiple markets noun
- The trader made a small fortune on arbitrage before lunch, and lost it again by the end of the day.
to practice arbitrage, as in the stock market verb
- People who are arbitraging can make a lot of money if they know what they are doing.