It’s not easy to formulate a definition that matches the brevity of this useful little word. It means to unfairly acquire a property by making a better offer than one that has already been accepted by the seller.
It takes up to three months in most parts of the UK to exchange formal contracts on the sale of a house. So there’s plenty of time for the gazumper to persuade the seller to accept his higher offer and unceremoniously dump the previous buyer who thought he had a firm agreement. Of course, it takes two to gazump — honest householders stick to their word. But at times when prices are rising rapidly or demand is high, cupidity is easily excited by a substantially improved offer. The term can also be applied to a form of sting by the seller in which the person who has agreed to buy is persuaded to increase their offer because of a real or fictitious claim that a better one has been made by somebody else.
In recent years, the term has been extend to overbidding on other kinds of contracts:
Back in 2006 a 14-year-old Neymar had a two-week trial at the club. They failed to follow through on their interest and the next time they tried to sign him he was seven years older and it would have cost them €150m to gazump Barcelona.
The Independent, 22 Jan. 2015.
Some dictionaries suggest gazump comes from the Yiddish gezumph, to overcharge or cheat. This is supported by the word’s first meaning in English back in the 1920s, to swindle, but others are less sure. These days it is always applied to house purchase and is used mainly in British or Australian English.
When the housing market is depressed, a stranger term appears, to gazunder, in which buyers arbitrarily reduce the offered price, usually near the date of exchange of contracts when there is little chance of the seller finding another purchaser. This appeared in the late 1980s, and is a rather curious blend of gazump and under. It has no connection with the colloquial use of gazunder for a chamber pot, so called because it usually “goes under” the bed.