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 (or perhaps a merger of it with the older, still dialectal form bire). Thus, between Latin and modern German, the word was reformed on the basis of the plural three times.
- → Estonian: pirn