An Etymological Dictionary of the German Language/Birne
Birne, f., ‘pear’; the n belongs properly to the inflexion; MidHG. bir (and still dialectic), plur. birn; OHG. bira, ‘pear.’ Derived from the Lat. pĭrum, or rather plur. pĭra. On account of the initial b of the German word, the date at which it was borrowed can hardly be placed earlier than the 9th cent. The Goth applied to the ‘mulberry-tree’ the apparently cognate term baírabagms. E. pear, AS. peru, Du. peer, are based upon the Rom. word (Ital. and Span. pera), derived from Lat. pirum. Respecting the change of gender see Pflaume.