Birne.

From Middle High German bire, bir, from Old High German bira, pira, from Vulgar Latin pira, reanalysis of the plural of Latin pirum. Early Modern German birn is from the Middle High German plural and dative/genitive singular, whence a double plural birnen was formed. The contemporary Birne is a new backformation from this plural (perhaps influenced also by the older, still dialectal form bire). Thus, between Latin and modern German, the word was reformed on the basis of the plural three times. Cognate with Alemannic German Bire. For the sense of "head", compare typologically Rübe, Russian ре́па (répa), ты́ква (týkva), коча́н (kočán), Italian zucca, Swedish knopp.