An Etymological Dictionary of the German Language/Pein
Pein, f., from the equiv. MidHG. pîne, pîn, OHG. pîna, f., ‘pain, punishment, torture’; adopted during the OHG. period on the introduction of Christianity from Lat. poena, which was pronounced pêna in MidLat. (comp. Ital. pena); MidLat. ê appears in HG. as î in other cases also (see Kreide and Feier), Comp. OSax. pîna, Du. pijn, AS. pîn, E. pine (a later variant of pain); also OIr. pían (gen. péne).