Make an oath is a phrase that refers to the act of swearing or making a solemn promise. It is usually done in a formal setting, such as a court of law, and involves the speaker raising their right hand and reciting a statement that they will uphold the truth of what they are saying. The crossword solution for this phrase is 'SWEAR', which is a verb meaning to make a solemn promise or vow. This phrase is often used in legal contexts, where it is necessary to make a binding promise to tell the truth.