What is another word for solemn oath?
Pronunciation: [sˈɒləm ˈə͡ʊθ] (IPA) 
A solemn oath is a promise or commitment made with great seriousness and importance. There are several synonyms that can be used in place of the term solemn oath, such as vow, pledge, assurance, undertaking, commitment, and covenant. Each of these words carries a similar weight of responsibility and dedication. A person who makes a vow or pledge is expected to keep their word and fulfill their promise. An assurance or undertaking is a guarantee that something will be done, while a commitment or covenant denotes a deep sense of obligation and loyalty. In all cases, the phrase solemn oath implies a deep conviction and a strong sense of honor and integrity.
