Decency and courtesy are synonymous with one another. Is it decent of someone to hold the door for you, or are they being courteous? When in reality it's both. To use references from other answers here: If women are sunbathing in Europe, it is a completely acceptable and decent act because it's legal. However, it would be courteous and decent if they were left alone and not harassed or ogled by other civilians. In the end, both words are built on the morality of the individual using them. So if the person using these words thinks that they are royalty, they may have higher than normal standards for everyone around them and if, for example, they are buying something and the cashier doesn't give them the best service they've ever had, they might think that they were intentionally being indecent or uncourteous. While someone with more modesty, who doesn't expect anything special from anyone may find decency/courtesy in someone who simply holds a door open for them or is simply nice. If you're looking for a clear separation between words defining "right and wrong", you should learn the difference between ethics and morals. Ethics are based on a society's rules (i.e. business ethics, police ethics, political ethics, etc.), while morals are built solely on the individual and may change depending on experiences they have.