An Etymological Dictionary of the German Language/Schwein
Schwein, n., ‘pig, hog,’ from the equiv. MidHG. and OHG. swîn, n.; corresponding to the equiv. OSax. swîn, Du. zwijn, AS. swîn, E. swine, OIc. svín, Goth. swein. These imply a primit. Teut. swîno-m, n., ‘pig,’ which must have been orig. a dimin. of Sau, ‘sucking pig, young pig’ (the OTeut. suffix -îna- was a favourite one in designating the young of animals; see Küchlein and Füllen), in the form of su-îna-m, ‘the young of the sow’ (primit. Teut. sû, ‘sow’). On account of the great prolificness of pigs, and hence the immense number of young pigs, the dimin. was used for the species?.