Source : Webster's Revised Unabridged Dictionary (1913)

Inappreciable \In`ap*pre"ci*a*ble\, a. [Pref. in- not +
   appreciable: cf. F. inappr['e]ciable.]
   Not appreciable; too small to be perceived; incapable of
   being duly valued or estimated. --Hallam.

Source : WordNet®

inappreciable
     adj : too small to make a significant difference; "inappreciable
           fluctuations in temperature"