The crossword solution for the term 'SWEAR UP AND DOWN' is AVER, which is a four-letter word. AVER is a verb that means to affirm or declare as true, often with confidence or emphasis. It is commonly used in legal contexts, such as when a witness swears to tell the truth in court. It can also be used to express strong conviction about something, such as when someone swears up and down that they are telling the truth.