Which word means to renounce or repudiate under oath?

The term that means to renounce or repudiate under oath is "abjure." Abjuration is a formal rejection or abandonment of a belief, cause, or claim, especially when done with an oath. This word is often used in legal contexts where an individual may renounce a previous commitment or allegiance, particularly in court or formal declarations.

The other options, while they may have their own meanings, do not convey the same sense of renunciation under oath. “Abdicate” refers to renouncing a throne or power, which is specific to a sovereign context. “Adhere” means to stick firmly to a surface or belief, which is the opposite of renouncing something. “Abate” refers to the reduction or diminishment of something, often used in terms of decreasing intensity or amount. Therefore, "abjure" is the appropriate term that encapsulates the act of renouncing or repudiating an oath.