Being one's duty to refers to an obligation or responsibility that one has towards something or someone. Antonyms for this phrase can include "optional," "unnecessary," "voluntary," "discretionary," "negligible," or "superfluous." When something is optional, it means that it is not required or essential. Similarly, when something is unnecessary, it means that it is not needed or compulsory. Voluntary refers to something that is done out of one's free will or without any obligation. Discretionary means that it is left to one's own judgment or choice. Negligible means that it is not significant or important, and superfluous implies something that is excessive or unnecessary.
