once-in-a-blue-moon

Spelling & Dictionary Insight

The English entry for once in a blue moon is 19 letters long, classified as anadv, and transcribed in the International Phonetic Alphabet as /wʌns ɪn ə bluː muːn/. It sits outside the most-frequent rank tiers, which is often why uncommon words generate more spelling variants per reader.The dominant gloss from Wiktionary reads: "Very rarely; very infrequently.".

No misspelling variants are generated for once in a blue moon in our index, suggesting the orthography follows predictable English patterns.It is not paired with a close-neighbour confusable in our dataset, which tends to mean the word is visually distinctive enough to stand on its own.

Etymologically, the entry records: See blue moon. First use appears c. 1833. See citation below. Root origin matters for spelling because borrowed morphemes (Greek, Latin, Old French, Old English) carry their source-language orthographic conventions into modern English, which is why historical etymology is often the cleanest predictor of whether a cluster like "-ough", "-eau", or "-tion" will appear. For readers arriving here from a spelling check, the authoritative guidance is: the correct English form is once in a blue moon, spelled O-N-C-E- -I-N- -A- -B-L-U-E- -M-O-O-N, and any other sequence of those letters, regardless of how natural it feels, is a misspelling in standard orthography.