Common courtesy is a term used to describe polite behavior that is expected in social situations. It is often seen as a sign of respect and kindness towards others. The four letter solution for the term common courtesy is 'ISNT'. This acronym stands for 'I Should Not Talk', which is a reminder to be mindful of what one says in order to maintain good manners. Common courtesy is an important part of everyday life, as it helps to create a more harmonious environment.