The word "jillions" is an informal term used to refer to an incredibly large number. However, there are several synonyms that can be used to express the same meaning. For example, the word "myriad" means a countless or extremely large number. "Multitude" is another synonym that refers to a vast number of items or individuals. "Countless", "innumerable", and "endless" are also synonyms that can be used instead of "jillions" to convey the idea of immeasurable quantity. Other options include "umpteen," "zillions," and "oodles," which are more playful but still communicate the concept of an overwhelming amount.