Definify.com
Webster 1913 Edition
Imponderable
Im-pon′der-a-ble
,Adj.
[Pref.
im-
not + ponderable
: cf. F. impondérable
.] Not ponderable; without sensible or appreciable weight; incapable of being weighed.
Im-pon′der-a-ble
,Noun.
(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.