'Imponderable' definitions:

Definition of 'imponderable'

From: WordNet
adjective
Difficult or impossible to evaluate with precision; "such imponderable human factors as aesthetic sensibility" [ant: ponderable]
noun
A factor whose effects cannot be accurately assessed; "human behavior depends on many imponderables"

Definition of 'Imponderable'

From: GCIDE
  • Imponderable \Im*pon"der*a*ble\, a. [Pref. im- not + ponderable: cf. F. impond['e]rable.] Not ponderable; without sensible or appreciable weight; incapable of being weighed. [1913 Webster]

Definition of 'Imponderable'

From: GCIDE
  • Imponderable \Im*pon"der*a*ble\, n. (Physics) An imponderable substance or body; specifically, in the plural, a name formerly applied to heat, light, electricity, and magnetism, regarded as subtile fluids destitute of weight but in modern science little used. [1913 Webster]