The term 'final authority' is used to describe a person or group that has the ultimate power to make decisions and enforce them. The crossword solutions for this term are SAY (3 letters) and SAYSO (5 letters). SAY is an informal way of saying something, while SAYSO is a more formal way of expressing an opinion or decision. Both words imply that the speaker has the final SAY in a matter, making them appropriate solutions for the term 'final authority'.