Cit! Mushroom! Counter hopper!
If you cut your teeth reading old regency romances like I did, you're probably familiar these terms. For those who did not, they represent a very particular form of class discrimination that was common in the upper classes of the 19th century and earlier. Gaining entry to the upper class wasn't a task one could accomplish simply by being rich. You had to be the right kind of rich, and those who made their money from the labor of their hands or sale of their goods were not welcome. Or, as so often happened when a titled person was in need of money, they were begrudgingly welcomed.
Regardless of the slurs being used, they all boiled down to the same upper class fear of the 'other' gaining entry to a very exclusive club. If someone could get in by wealth alone, that opened the door to a near endless list of potential gatecrashers.
But, if it wasn't acceptable to make money through trade or work, how on Earth did the upper class maintain any kind of wealth? Well, a man had limited options if he wanted to maintain his reputation and still be called a gentleman. Our modern ears hear the word gentleman and think polite, kind, well mannered; the term had a much more specific meaning, once upon a time. A gentleman was, first and foremost, idle. If you worked, you were no gentleman.
The Land Lord: The most approved form of wealth for the upper class was land ownership and rents. As the most idle form of income imaginable, this is the very definition of 'no work'. Unfortunately, it could also be the most unstable. A bad turn in the weather could destroy crops, thus impoverishing the tenants and making them unable to pay their rent. Even the rich lord of the manor can't bleed a stone.
The Percents: Making money from money. The rich would place the vast majority of their capital into bank account that issued returns as a percent, essentially an annuity. They would live off the annuity alone, not spending the actual principal amount. At least, this was what the smart ones did. More than one upper class family was ruined when the patriarch outspent his income and was forced to chip away the principal to pay debts. In Jane Austen's novel, you often hear someone's income described as an annuity, "He has fifty thousand pounds in the six percents." Etc.
Dowries (marrying money): It was easier for a woman to rise in society than a man, since women essentially left their families and joined new ones upon marriage. Because of this, a broke man with maybe a title or grand familial connections could marry a rich girl from one of those "vulgar" merchant families and prop up his dwindling wealth. Pointing out the hypocrisy of disdaining merchant money while taking it in the form of a dowry would be pointless. The regency upper classes were connoisseurs of hypocrisy.
Military & Clergy: These were the only 'professions' deemed acceptable for the sons of gentleman, jobs they could hold and still keep their status. If you were a second or third son with no inheritance coming to you, this was your most likely path (unless your family name was grand enough to attract one of those rich merchant class girls). Still, it should be noted that if a man relied entirely on his military or clerical salary to live, he fell significantly in stature. Wealth was still important, after all.
Other professions such as the law and government service were acceptable, but they placed a man at the fringes, and unless he was able to marry up it was likely his children would drop down into the merchant class and float away from the top.
Viewed with the historical perspective.
The best way to read historical fiction is through the lens of the time period itself. If you step into a regency romance with 21st century expectations, you are likely to be disappointed. It is easy for us to sneer at the money troubles of a gentleman and say, "Get a job!" when we consider the hundreds of thousands of working class people below that gentleman. We feel uncomfortable having sympathy for a character who, by every comparison to our modern society, would have been so privileged and coddled that it almost boggles the mind. We must struggle to understand a long gone world in which people were born into structures and never taught how to live outside of them. Men and women raised with narrow educations and abilities, coupled with an ingrained fear and shame of doing anything outside that structure. Reputation was everything, to a degree that we today would be hard pressed to understand. It would take a incredibly strong person to give up their friends, society, to risk embarrassing their family and becoming and object of derision, all for the sake of stepping outside the structure for money. This is where genteel poverty comes from. The social penalties for stepping outside the structure, for working, were such that some families chose to live hand to mouth on the scraps of their dwindling wealth rather than work.