Difficult or impossible to comprehend or evaluate.
Not ponderable; without sensible or appreciable weight; incapable of being weighed.
An imponderable question.
A factor that cannot be anticipated.
An imponderable substance or body; specifically, in the plural, a name formerly applied to heat, light, electricity, and magnetism.
Open and not yet settled or determined.
Uncommitted, not having reached a decision.
A voter etc. who has not yet come to a decision.