noun
1. : a very long period of time — usually used in the phrase once in a blue moon
such people happen along only once in a blue moon — Saturday Review
2. : the rare blue appearance of the moon that is due to dust particles in the high atmosphere
noun
1. : a very long period of time — usually used in the phrase once in a blue moon
such people happen along only once in a blue moon — Saturday Review
2. : the rare blue appearance of the moon that is due to dust particles in the high atmosphere
Webster's New International English Dictionary. Новый международный словарь английского языка Webster. 2012