oro-

a mountain nymph," "1580s, from Latin Oreas (genitive Oreadis), from Greek Oreias "mountain nymph," from oros "mountain, height," also (in Egypt) "desert," in contrast to the cultivated plain, probably from PIE *heros- "elevation." Also see -ad. Attested in English from late 14c. in Latin plural form Oreades. An Old English word for a similar thing was dunælfa ("mountain elf").

1890, "mountain-forming, the formation of mountains," from French orogénie; see oro- + -geny. In reference to particular mountain-building geological periods, by 1914. Related: Orogenic (1886); orogenesis (1886).