An oath taker's pledge is a promise of LOYALTY. It is usually made in the form of an oath, which is a solemn and formal declaration of commitment to a particular cause or belief. The term 'oath taker's pledge' can be used to refer to any type of promise of LOYALTY, such as a military oath, a marriage vow, or a promise to uphold the law. The crossword solution for this term is 'LOYALTY', which is a seven-letter word that accurately describes the nature of an oath taker's pledge.