Ethics vs. morals
Morals are the principles on which one’s judgments of right and wrong are based. Ethics are principles of right conduct. So the two nouns are closely related and are often interchangeable. The main difference is that morals are more abstract, subjective, and often personal or religion-based, while ethics are more practical, conceived as shared principles promoting fairness in social and business interactions. For example, a politician’s sex scandal may involve a moral lapse (a subjective judgment), while a politician taking money from a company he is supposed to regulate is an ethical problem. But of course, both ethics and morals may have a part in both situations.
Ethics (the word takes a plural form but is treated as singular) is also a field of philosophical study. There aren’t many college courses on morals (though ethics courses inevitably involve discussions of morals), whereas classes in ethics are required for many degrees, especially in law, business, and medicine.
Meanwhile, the difference between ethics and morals is often formulated this way: that ethics are the science of morals, and morals are the practice of ethics. But that’s a little too neat and doesn’t cover all the ways in which the words are used.