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.
Im*pon"der*a*ble (?), a. [Pref. im-
not + ponderable: cf. F. impondérable.]
Not ponderable; without sensible or appreciable weight;
incapable of being weighed.