Sentence:  Sudden fortunes, indeed, are sometimes made in such places, by what is called the trade of <WSD>speculation</WSD>. 
Meaning of the word marked with <WSD> tags:  The act or practice of buying land, goods, shares, etc., in expectation of selling at a higher price, or of selling with the expectation of repurchasing at a lower price; a trading on anticipated fluctuations in price, as distinguished from trading in which the profit expected is the difference between the retail and wholesale prices, or the difference of price in different markets.