The cgs unit of work or energy (3)
I believe the answer is:
erg
I believe this clue is a double definition.
'the cgs unit of work' is the first definition.
(I've seen this in another clue)
'energy' is the second definition.
(Other definitions for erg that I've seen before include "Unit of work or energy" , "shifting sand" , "Unit of measurement of work" , "Unit of work; dunes area" , "Unit of work (phys.)" .)