An Etymological Dictionary of the German Language/Annotated/Schwein
Schwein, neuter, ‘pig, hog,’ from the equivalent Middle High German and Old High German swîn, neuter; corresponding to the equivalent Old Saxon swîn, Dutch zwijn, Anglo-Saxon swîn, English swine, Old Icelandic svín, Gothic swein. These imply a primitive Teutonic swîno-m, neuter, ‘pig,’ which must have been originally a diminutive of Sau, ‘sucking pig, young pig’ (the Old Teutonic 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’ (primitive Teutonic sû, ‘sow’). On account of the great prolificness of pigs, and hence the immense number of young pigs, the diminutive was used for the species?.