The term gentleman is often used sarcastically or satirically in David Copperfield. Sometimes it just refers to anyone, but other times it refers to a specific social class. In chapter 25, Dickens refers to “professional gentlemen” in Doctors’ Commons. These are individuals that don’t do much but sit around and talk.
The first real reference to the definition of gentleman is in chapter 3, when David is comparing his orphanhood to Emily’s.
'Besides,' said Em'ly, as she looked about for shells and pebbles, 'your father was a gentleman and your mother is a lady; and my father was a fisherman and my mother was a fisherman's daughter, and my uncle Dan is a fisherman.'
She also describes what treasures she would buy for her uncle if she were a “lady”. The implication, for Emily at least, is that a lady has money and standing.
The second exchange that relates to the definition of gentleman is between Mr. Mell and Steerforth in chapter 7.
'I don't give myself the trouble of thinking at all about you,' said Steerforth, coolly; 'so I'm not mistaken, as it happens.'
'And when you make use of your position of favouritism here, sir,' pursued Mr. Mell, with his lip tremblingvery much, 'to insult a gentleman -'
'A what? - where is he?' said Steerforth.
Steerforth insults Mr. Mell, but saying that he is not a gentleman. Steerforth continuously belittles Mr. Mell and eventually campaigns to get him fired. By implying that Mr. Mell is not a gentleman, Steerforth brings him down below the level of the students.
Uriah Heep further expounds on the concept of gentleman, with characteristic false modesty:
You think it justifiable, do you, Copperfield, you who pride yourself so much on your honour and all the rest of it, to sneak about my place, eaves-dropping with my clerk? If it had been ME, I shouldn't have wondered; for I don't make myself out a gentleman (though I never was in the streets either, as you were, according to Micawber), but being you! –
Therefore, while the definition of gentleman is mostly related to money, it can also relate to character. A gentleman is not just someone who has money, but also someone who can be trusted.