The term was first used by Adam Sedgwick in 1847 with reference to the "Arenig Ashes and Porphyries" in the neighbourhood of Arenig Fawr, in Merioneth, North Wales.
Arenig
- (geology) A time interval during the Lower Ordovician period.
- Synonym: Arenigian
- gainer, Gearin, anigre, Regina, regian, regain, Angier, Reagin, inrage, raigne, regina, Negari, earing, reagin, Gainer, graine, Aigner, in gear
