Duke Xi of Lu reigned in the Spring and Autumn period.
Tips
history
僖 is not used independently in modern Chinese. It meant joyful, essentially a 人-side writing of 喜, and survives mainly as a posthumous temple title of rulers such as 鲁僖公 and as a surname.
register
Historical and onomastic; you see it in dynastic names and old records, not in speech.
