鏡開き

プログレッシブ和英中辞典(第4版)

かがみびらき【鏡開き】

the custom of cutting and eating a large, round rice cake, which had been offered to the gods at New Year's, on January 11

講道館の鏡開き
the first training session of the New Year at the Kodokan Sports Center

出典　小学館「プログレッシブ和英中辞典(第4版)」