"wealth, riches, affluence," c. 1500, from French opulence (16c.), from Latin opulentia "riches, wealth," from opulentus "wealthy," a dissimilation of *op-en-ent-, which is related to ops "wealth, power, ability, resources," and to opus "work, labor, exertion" (from PIE root *op- "to work, produce in abundance").
Opulence is a dignified and strong word for wealth. Wealth and riches may mean the property possessed, and riches generally does mean it; the others do not. Affluence suggests the flow of wealth to one, and resulting free expenditure for objects of desire. There is little difference in the strength of the words. [Century Dictionary, 1895]