From Wiktionary, the free dictionary
See blue moon . First use appears c. 1833. See cite below.
IPA (key ) : /wʌns ɪn ə bluː muːn/
once in a blue moon (not comparable )
( idiomatic ) Very rarely ; very infrequently .
Synonyms: see Thesaurus:rarely
Coordinate term: once in a purple moon
1833 , J. Lection (publisher), The Athenæum , page 780 :We are no advocates for the eternal system of producing foreign operas to the exclusion of the works of English composers, but once in a blue moon such a thing may be allowed.
1933 , James Hilton , Lost Horizon , published 1973 , page 133 :[T]ime expanded and space contracted, and the name Blue Moon took on a symbolic meaning, as if the future, so delicately plausible, were of a kind that might happen once in a blue moon only.
very rarely
Chinese:
Cantonese: 千載難逢 / 千载难逢 ( cin1 zoi2 naan4 fung4 ) , 十年唔逢一閏 / 十年唔逢一闰 ( sap6 nin4 m4 fung4 jat1 jeon6 )
Mandarin: 千載難逢 / 千载难逢 (zh) ( qiānzǎinánféng )
Czech: jednou za uherský rok (cs)
Dutch: eens in de zoveel tijd
Esperanto: ege malofte
Finnish: todella harvoin
French: tous les trente-six du mois (fr) ( on every thirty-sixth day of the month ) , une fois toutes les lunes
Georgian: ათასში ერთხელ ( atasši ertxel )
German: alle Jubeljahre (de)
Greek: στη χάση και στη φέξη (el) ( sti chási kai sti féxi )
Irish: uair sna naoi n-aird , uair umá seach
Italian: una volta ogni morte di papa , ogni morte di papa
Japanese: ごくまれに ( gokumare ni )
Polish: raz na ruski rok (pl) , od wielkiego dzwonu (pl)
Portuguese: de vez em nunca (pt) , uma vez na vida, outra na morte
Russian: раз в сто ле́т ( raz v sto lét ) ( once every hundred years )
Scottish Gaelic: uair san ràith
Slovak: raz za uhorský rok
Spanish: cada muerte de obispo (es) , de guindas a brevas , de higos a brevas , de Pascuas a Ramos (es) , de ciento a viento (es) , de ciento en viento (es)
Thai: มากไม่ค่อย
Turkish: kırk yılda bir