Source : Webster's Revised Unabridged Dictionary (1913)

Erg \Erg\, n. [Gr. ? work.] (Physics)
   The unit of work or energy in the C. G. S. system, being the
   amount of work done by a dyne working through a distance of
   one centimeter; the amount of energy expended in moving a
   body one centimeter against a force of one dyne. One foot
   pound is equal to 13,560,000 ergs.

Source : WordNet®

erg
     n : a cgs unit of work or energy; the work done by a force of
         one dyne acting over a distance of one centimeter