im·pon·der·a·ble /(ˌ)ɪmˈpɑnd(ə)rəbəl/
 (a.)無重量的,無法計算的,不可估價的無法測知重量的事物
 Im·pon·der·a·ble a.  Not ponderable; without sensible or appreciable weight; incapable of being weighed.
 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.
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 imponderable
      adj : difficult or impossible to evaluate with precision; "such
            imponderable human factors as aesthetic sensibility"
            [ant: ponderable]
      n : a factor whose effects cannot be accurately assessed; "human
          behavior depends on many imponderables"