erg (n.1)

unit of energy in the C.G.S. system, coined 1873 by the British Association for the Advancement of Science, from Greek ergon "work," from PIE root *werg- "to do."

erg (n.2)

"region of drifting sand dunes," 1875, from French erg (1854), from North African Arabic 'irj, from a Berber word.