The word "jillion" is an informal term used to describe an extremely large number or quantity. However, it is not a formal word and has no official antonyms. Nevertheless, we can use different words to imply the opposite meaning of "jillion". For example, the word "few" describes a small number or quantity. Another option could be the word "scant", which implies a limited or insufficient amount. Additionally, the word "meager" describes an inadequate or sparse amount of something. The antonyms of "jillion" depend on what context you use it. Therefore, it is essential to choose an appropriate word that conveys your intended meaning explicitly.