erg (n.1) Look up erg at Dictionary.com
unit of energy in the C.G.S. system, coined 1873 by the British Association for the Advancement of Science from Greek ergon "work" (see organ).
erg (n.2) Look up erg at Dictionary.com
"region of drifting sand dunes," 1875, from French erg (1854), from North African Arabic 'irj, from a Berber word.