Antonyms for the phrase "be one's duty to" are "be optional," "not be required," and "be unnecessary." These words convey the opposite of obligation or responsibility. When something is optional, it is up to one's discretion whether to do it or not. Whereas, when something is not required, there is no obligation or necessity to complete it. Similarly, when something is unnecessary, it is not needed or required to be done. Antonyms for "be one's duty to" helps us understand that sometimes we have the choice to take action or not, and it is not always a matter of obligation.
