The antonyms for the word "casting up" are "casting down," "lowering," "dropping," or "decreasing." These words all convey a sense of reducing or bringing down something, rather than elevating or increasing it. In contrast to casting up, casting down is often associated with negative connotations, such as demotion, devaluation, or a decline in one's fortunes. The word lowering implies a deliberate act of bringing something to a lower level, while dropping connotes an unplanned or sudden decrease. Finally, the word decreasing simply refers to a gradual or intentional reduction in the amount, value, or intensity of something.