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blue moon event

blue moon event

6.6
A very rare event that almost never happens
  • noun
  • Informal
translation icon : evento raro
  • Her research, published in the November issue of the journal Risk Analysis, suggests that other fields could borrow risk analysis strategies from engineering to make better management decisions, even in the case of once-in-a-blue-moon events where statistics are scant, unreliable, or non-existent.

Examples

  • Winning the lottery is a blue moon event that very few people experience in their lifetime.

  • Finding a four-leaf clover is considered a blue moon event because it is so rare.

  • The once-in-a-lifetime concert turned out to be a blue moon event that everyone wanted to attend.

Synonyms

blue moon
vsblue moon event
  • Informal
7 6.1

An event that happens very rarely

is identical in meaning but uses a longer explicit phrasing

How Rare

one-off
8 5.6
blue moon event
  • Informal
6.6
rare
582 4.1
infrequent
13 4.5
occasional
285 2.8
common
797 1.0

Surface Forms

Morphology

blue + Moon + event

Knowing 'blue' (a color), 'moon' (the satellite) and 'event' (an occurrence) does not lead naturally to the meaning 'very rare'; the sense of rarity comes from the idiomatic phrase 'once in a blue moon', a conventionalized metaphor rather than a transparent composition. Because the rarity sense is culturally encoded and not predictably derivable from the parts, learners who know the words but not the idiom will likely not infer the intended meaning.

Etymology

Blue moon event comes from the old idea of a blue moon. One popular story says smoke or dust sometimes made the moon look blue, so seeing one was very rare, and 'a blue moon event' now means 'very rare'.