If you say that one thing happens courtesy of another or by courtesy of another, you mean that the second thing causes or is responsible for the first thing. The air was fresh, courtesy of three holes in the roof As millions will have seen, by courtesy of the slow motion re-runs, the referee made a mistake
A courtesy call or a courtesy visit is a formal visit that you pay someone as a way of showing them politeness or respect. The President paid a courtesy call on Emperor Akihito
Courtesy is used to describe services that are provided free of charge by an organization to its customers, or to the general public. A courtesy shuttle bus operates between the hotel and the town. a courtesy phone
politeness, as in: Your staff extended me every courtesy during my stay at your hotel
Favor or indulgence, as distinguished from right; as, a title given one by courtesy
The right which a husband by law in his deceased wife's estate; applicable in only a few states