imponderable(n = noun.cognition) - a factor whose effects cannot be accurately assessed; "human behavior depends on many imponderables"
is a kind of influence
has particulars: leaven, leavening

   imponderable(a = adj.all) - difficult or impossible to evaluate with precision; "such imponderable human factors as aesthetic sensibility"
Antonym: ponderable

   Not ponderable; without sensible or appreciable weight; incapable of being weighed. [1913 Webster]

   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]

imponderable, adj. & n.
--adj.
1 that cannot be estimated or assessed in any definite way.
2 very light.
3 Physics having no weight.
--n. (usu. in pl.) something difficult or impossible to assess.

Derivative:
imponderability n. imponderably adv.

N  levity, lightness, imponderability, buoyancy, volatility, feather, dust, mote, down, thistle, down, flue, cobweb, gossamer, straw, cork, bubble, balloon, float, buoy, ether, air, leaven, ferment, barm, yeast, lighter-than-air balloon, helium balloon, hydrogen balloon, hot air balloon, convection, thermal draft, thermal, light, subtile, airy, imponderous, imponderable, astatic, weightless, ethereal, sublimated, gossamery, suberose, suberous, uncompressed, volatile, buoyant, floating, portable, light as a feather, light as a thistle, light as air, lighter than air, rise like a balloon, float like a balloon.