Rich, wealthy, affluent, opulent are applied both to persons and to things.
The last three are close synonyms of rich, the general term, but they are more explicit in their implications and more limited in their range of application.
One is rich that possesses more than enough to gratify normal desires and needs. Rich, therefore, may describe anyone or anything above what is felt as average or normal in possessions. When used of persons, without qualification, it implies the possession of money or of property, especially income-producing property.
In its extended use one may be rich in friends, in talents, or in interests; a soil may be rich in nitrogen; a poem may be rich in meaning, a career in promise, a flower in fragrance. Also, something is rich which is above the line dividing the cheap from the costly or precious or dividing the stinted in elements or ingredients from the bountifully supplied.
One is wealthy that possesses money, income-producing property, or intrinsically valuable things in great abundance. Wealthy is rarer than rich in extended use and usually connotes material possessions. It also more often than rich implies a way of living in keeping with one’s income and a commanding position in the community, state, or world.
One is affluent that is prosperous and therefore continually increasing one’s material possessions.
Affluent , though often used to describe persons, groups, or nations, is more often applied to their circumstances or to their state; thus, a rich man is in affluent circumstances if his income is increasing or, at least, not decreasing; one is reduced from an affluent position but not from riches or wealth, for only affluent implies increase and therefore suggests decrease as its opposite.
One is opulent that is ostensibly and ostentatiously rich; thus, a person in affluent circumstances may or may not maintain an opulent establishment, for affluent suggests the inflow of money and opulent lavish expenditure. Hence opulent usually qualifies things that are luxurious, prodigal, expensively splendid, or sumptuous.
When applied to persons opulent usually qualifies a specific term which harmonizes with it in implications. Occasionally opulent does not connote display but inexhaustible richness.