Source : Webster's Revised Unabridged Dictionary (1913)

Crith \Crith\ (kr?th), n. [Gr. ??? a barleycorn, a small
   weight.] (Chem.)
   The unit for estimating the weight of a?riform substances; --
   the weight of a liter of hydrogen at 0? centigrade, and with
   a tension of 76 centimeters of mercury. It is 0.0896 of a
   gram, or 1.38274 grains.

Source : WordNet®

crith
     n : the weight of a liter of hydrogen (at 0 Centigrade and 760
         millimeters pressure)