Patronise – is a homograph, with two seemingly very different meanings; it is to be a customer of a place (usually a pub) and to treat someone condescendingly.
How has this word come to have two meanings which are so different? The origin of both is the Latin word ‘pater’ meaning ‘father’, it was applied by the Roman’s to well-off people, helping out people from the poorer classes as a form of charity; they would apply their support to one or two people to help with education and social standing. The rich people tried to teach their protégés manners and social ettiquette and the poorer people, indebted to their patrons, would be unable to point out that their lessons were very basic, due to fear of their support being removed.
Then, in a simlar way in the 17th century, the word ‘patron’ began to be used to describe rich customers who supported artisan shops by making large and/or frequent purchases. It later began being applied more broadly, and now can be used to describe any customers.