Factors, causes, or elements that contribute to a result that are difficult or impossible to estimate or to assess: There are simply too many imponderables for an accurate prediction about what will happen in the European Union if any of the countries were to default their debts.

Some imponderables are nothing more than notions without any motions.

Difficult or impossible to estimate, to assess, or to answer: There are some imponderable problems regarding the understanding of a philosophy that involves the study of ideas about life, existence, and other issues that are not part of the physical world.