once in a blue moon

adv.

千载难逢地；俟河之清；百年不遇；

Once in a blue moon
Once in a blue moon
Once in a Blue Moon
Inadvertent chlorpropamide hypoglycemia--no longer once in a blue moon?
Cutaneous metastasis in endometrial cancer: once in a blue moon – case report
Once in a Blue Moon: Airmen in Theater Command
Once in a blue moon: detection of 'bluing' during debris transits in the white dwarf WD1145+017
Once in a Blue Moon … Rare Adnexal Tumor: From the Clinical and Videodermoscopical Aspects to the Mohs Surgery and the Histological...
Once in a Blue Moon Lodge: A Novel
Once in a Blue Moon Lodge
The origin of the expression “once in a blue moon”. Can the moon really be blue?
Once in a Blue Moon Lodge: A Novel
Once in a Blue Moon Lodge: A Novel