Calendars, as we know, are systematic arrangements of days and months in a year. However, when it comes to finding antonyms for the word "calendars," we have to delve into some words that are not directly related but hold opposite meanings. For instance, "disarray," "confusion," "ouranomancy," "upheaval," and "irregularity" are some of the antonyms for the term "calendars." The term "disarray" refers to a state of disorganized confusion, while "upheaval" means a violent change or disturbance. "Ouranomancy" is the art of divination by interpreting the sky while "irregularity" is the absence of regularity or conformity to set standards.