(generally called Nabob). Corruption of the Hindu word nawab, the plural of naib. An administrator of a province and commander of the Indian army under the Mogul Empire. These men acquired great wealth and lived in Eastern splendour, so that they gave rise to the phrase, “Rich as the nawâb,” corrupted into “Rich as a nabob. ” In England we apply the phrase to a merchant who has attained great wealth in the Indies, and has returned to live in his native country.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894