imponderable

adjective

1. not ponderable; that cannot be precisely determined, measured, or evaluated.

noun

2. an imponderable thing, force, agency, etc.

adjective

1. unable to be weighed or assessed

noun

2. something difficult or impossible to assess

adj.

1794, “weightless,” from assimilated form of in- (1) “not, opposite of” + ponderable (see ponder). Figurative use, “unthinkable,” from 1814. Related: Imponderably. As a noun, by 1842.